Formula for kWh Calculator

kWh CalculatorFor those of you out there wanting to save electricity one of the formulas you will need to know is the formula to calculate your kWh usage or elecricity usage. This way you know what each device in your home is using. So you know where you can cut your costs in your home. The information found here will teach you what is a kilowatt hour, how to calculate kWh, convert watts to kWh, and more!

First of all kWh stands for Kilowatt Hours. This is usually what you will see on your electricity bill or electricity statement when you receive it. The electric comany knows how much electricity you are using by reading your kWh meter. You will also have the electricity cost per kWh listed on your electric bill so you know what each kWh is costing you.

A kilowatt hour is a measurment of how many kilowatts are used in a hour. Most electrical devices will have printed on them how many watts they are using, which it takes 1000 watts to equal 1 kilowatt. So a 1000 watt microwave oven running for 1 hour will use 1 kWh.

Watts is  a measurement of how much electricity that electrical device uses constantly, where kilowatt hours is how many watts that electrical device has accumulated over time. For example a 60w incandescent light bulb in your closet will use 60 watts everytime it is turned on. But if it is turned on an hour a day while you pick out your clothes that’s 30 hours that light has been on that month. That’s 1,800 watt hours or 1.8 kilowatt hours. Continue reading this information on how to calculate kWh to get the formula used to calculate your kWh usage

But for those of you that are wanting to calculate what each electrical device in your home is using then you will need to use this formula to calculate the kWh usage in your home:

( Watt Usage * Hours/Day * Days/Mo. ) / 1000 = Kilowatt Hours used that month

So for an example we have a normal incandescent light bulb that uses 60w, that we have on 16 hours every day of the month. So I can calculate how many kWh this incandescent light bulb is using every month by using this formula:

60w * 16 hours/day * 30.5 days/mo / 1000 = 29.28 kWh per month

After you know how many kilawatt hours a device is using you can multiply this kWh by the cost per kWh that is stated on your electric bill:

kWh * Cost/kWh = Cost per month

So using the 60w incandescent light bulb example, which was using 29.28 kWh/mo.:

29.28 kWh * $0.10/kWh = $2.928/mo.

So a single 60w incandescent light bulb will cost you $2.93/mo.

NOTE: This is based on $0.10/kWh and also I have the amount of days per month 30.5, I figured this way I don’t have to figure out if this month is 30 days or 31 days.

You have to know how many watts a device is using before you can use any of the formulas found in the information above. Most devices will have the wattage printed on the electrical device somewhere. If your electrical device does not have the wattage printed on it but it does have amperage printed on it, please look at Volt Amp Watt Convert to learn how to convert amps to watts. If your electrical device does not have amperage or wattage printed on it, then you will have to learn How to Measure Amperage with a Multimeter.

For those of you that find calculating your kWh usage using the kWh formula too complicated you can purchase a kWh meter to measure kWh usage.

For anyone that would like to use Go Green in Your Home’s kWh calculator you can check out Calculator to Calculate Kwh

Thank you for reading this information on How to Calculate kWh on Go Green in Your Home. Go Green in Your Home hopes this information has helped you calculate each of your electrical devices kWh usage so you know how much electricity you are using. For more tips on how to save electricity or save the environment continue reading through Go Green in Your Home!

124 Responses to “Formula for kWh Calculator”

  1. Go Green In Your Home Says:

    This depends on the efficiency of the transformer. If you are wanting to use 230VAC primary and 120VAC secondary on the transformer, the watts will be very similar. 110VAC with 4amp is 440 watts, which on the primary side of the transformer will be 230VAC with atleast 1.91 amps being drawn (440watts). Again, that’s at 100% efficiency of the transformer. I’m sure there will be a slightly higher current draw on the primary side than the 1.91 amp as your transformer will not be 100% efficient. Thanks for visiting.

  2. Liyanage Says:

    Hello from Sri Lanka we are use of 230 voltage
    (110-120V 60Hz 4.0A)
    My problem is
    (110-120V 60Hz 4.0A) how mach the watts.use of transformer?

    Please reply
    Thanking You

  3. Go Green In Your Home Says:

    I forget the formula off the top of my head, but there was quite a bit involved, the efficiency of the hot water tank, ambient temperature, gallons, then the formula was something like it takes xxx BTU to heat 1 gallon to xxx temp.. I’ll see if I can find it again.

  4. bill cudnyj Says:

    Friend has a hot water leak, I’m going to say 50 gallon hot water heater. How would I figure out what her cost is for the gas on that HWH running 24 hours a day ?

  5. Luther Curtis Says:

    Hi, the whole thing is going well here and ofcourse every one is sharing information, that’s genuinely fine, keep up writing.

  6. frank Says:

    can you tell me how much my monthly price per kw will go up over 20 years given its current price is .20 per kw and it goes up 8% per year? ie: 1st year..20 2nd year .20 x 8% etc do you have a calculator to calculate the next 20 years ?

  7. Go Green In Your Home Says:

    I can’t give you an exact number, but I can give you an average. Just take 2500 kWh and divide by 30.5 days, that won’t tell you exactly what eachbday uses, but average overall. Hope that helps. 81.97 kWh each day.

  8. colin Says:

    My power bill on avarice says 2500kwh used
    I am trying to calculate that into what’s used per day.
    This is such a great site and I research lots on here as I am building a new house off grid.
    Well it’s getting close to having to decide on my solar set up.
    Thanks for the help.

  9. Go Green In Your Home Says:

    If the generator is 1,000 watts, running for 1 hour would be 1kWh. You will reach 1,000watts as soon as you reach 400rpm. Deep cycle batteries are best used. As far as capacity of the batteries, this depends on how long you want to be able to use power, and what kind of power you are pulling on your load.

  10. Tariq Says:

    Dear Sir,
    if i have 1kw PM-generator @ 400 rpm, i want to drive it with animal power with gearbox, if i reached 400 rpm, how many hours will take to get 1000w(1kw) power.
    + which kind of batteries and what capacity of batteries i need to store 1kw, without grid connection. ?
    best regards

  11. Jaco Says:


    If I want to calculate the KWh of a watt load that changes all the time like my house power. Will it work if I record the total watts every minute. Then after 60 minutes add all the values up and the / 1000 to get the KWh for that hour. You keep on doing that until you have 24 hours to make up a full day. Then you add all the hours to get the total for the day.

    Regards Jaco

  12. Go Green In Your Home Says:

    I need more information from you. I need to convert 10 amps to watts. To do so that’s Amps x Volts = watts so is this 10 amps on 12vdc, 120vac, 220vac, 480vac?

  13. H.A Says:

    Please I would like an answer to the following
    I have a 10 amperes meter.
    My question is: If I utilize it full for 20 hours, how many kilowatts would I have utilized?
    Thank you in advance.

  14. Muhammad Rehan Says:

    My question is.
    What is the maximum value of a load which consume 500 KWh per day at a load factor of 0.40, if the consumer increases the load factor of 0.50 without increasing the maximum demand?

  15. Go Green In Your Home Says:

    You can use the calculator on my site to do this. Just enter your values and it will calculate. But, if that’s really 50kW generator and not 5kW generator and your generator runs 24 hours a day, every day, you should be generating 10 times the amount you need. So within about a week you should have enough electricity generated to last the entire month. If its a 5kW generator you will just break even about every month.

  16. David Says:

    My power company will store unused energy generated by green energy and credit back to me when im not generating I use 3500 kWh of power a month if i have a 50kw generator run by water wheel how long will it have to run to get my monthly amount of energy

  17. Go Green In Your Home Says:

    You could use the formula I have provided to calculate each second then add them together. 1 second is 0.000277778 hours, so if your sensor is reading 10, 5, 19 you could calculate each one using 0.000277778 hours as your time, then add up each of those calculations to give you your kWh. You can also add up all 3,600 readings, divide by 3,600 (giving average watts) then use that with my kWh formula. So ((SUM-OF-YOUR-3600-READINGS/3600)*1)/1000 = kWh Which since it’s for only 1 hour, you can leave out the *1 and just do (SUM-OF-YOUR-3600-READINGS/3600)/1000 = kWh. Yes, you are right, this will give you the average used during that hour, but at the same time, this will be the amount that would have been used constantly for that entire hour, giving you the accumulated kWh.

  18. owen khosa Says:

    hi there

    here are my Questions

    1.find out how Eskom or municipality charge out electricity? much power does a 1 kw generator give if the generator is on for 24hours a year?

    3.if the generator uses 1 litre per hour how much would your cost be for 1 unit if it may on for 24hour ayear?

    owen khosa

  19. Rich Says:

    The units and formulas all make sense to me – but I’m still confused how to accumulate kWh for something I’m measuring.

    If I have a sensor which takes a reading of Watts every second – how do I calculate my usage for an hour?

    For example, if I total up those values and divide by 3,600 (60min * 60sec), aren’t I just getting an AVERAGE usage for the hour and not actual accumulated?

    Thanks for shedding any light on this for me :)

  20. Go Green In Your Home Says:

    Here is a calculator to calculate your kWh

  21. saran Says:

    Dear all,

    Anyone can help me to find the below, please

    A bungalow unit with 1500sq ft floor area at 2VA/sq ft, 12,000 VA electric range, 4500 VA heater, 1200 VA dishwasher, 5000 VA clothes dryer, 1035 VA kitchen waste disposer, and 10,000 VA of separately controlled electric baseboard in six rooms. Using the Demand Factor at 100% is 3000 VA and Remaining Load at 40%. Determine the Kwhr consumption of the unit.


  22. Jalil Says:

    Kopana you are wayyyyy smarter than me. Can you please call me???? I need your regarding how to calculate using your formula. Please!!


  23. Go Green In Your Home Says:

    Do you mean what is the average power usage for water pump for a geyser or do you mean a nature geyser?

  24. kopano Says:

    what is the average power usage of a geyser

  25. Go Green In Your Home Says:

    This depends on how you’re converting the diesel to electric. How many watts your generator puts out, the generator’s efficiency, etc.

  26. ebinum Says:

    how do i convert 600 litres of diesel to kwh?

  27. Mel Says:

    I just wanted to know on How to determine the average energy (kwh)of a buildings in one compound; For examples;
    My compound total energy used was 100, 000 kWh / month, and
    then, within the compound I have associated
    Buildings A: 5000 kwh consumed / month
    Building B : 6000 kWh consumed /month
    Building C : 10,000 kWh /month

  28. Go Green In Your Home Says:

    228W panel is constant.. Meaning in optional light conditions the solar panel is generating 228W in that moment. If this single solar panel was in optimum lighting conditions for 1 hour the panel will generate 228Wh so yes to generate 1KWh you would need 5 solar panels, which would generate 1.14KWh every hour that the panels are in optimum sun light.

  29. Lety Says:

    Hello!! I am looking at solar panel specifications, and the NOCT Maximum Power of a Panel is 228W. Is this 228W per hour of sunlingt under NOCT conditions?

    This way, if I would like to generate 1KWh (before I take away the losses due to the inverter) I would need around 4-5 panels.

    Is this correct?

  30. pankaj Says:

    i neeed kwh calculator

  31. Lee Says:

    Thank you for this wonderful site. Just the answers to the questions has helped me understand more than I have been able to get from my electricity companies.

  32. Go Green In Your Home Says:

    Oh, must have forgotten to add in the 1000. I look it over when on PC. I’m on phone and hard to edit while using it. Thanks for the info.

  33. Paul Says:

    Your formula in the calculator is not correct. W x H x 365.25 / 12 does not equal kWh/Mo. It equals Wh/Mo. You then need to divide by 1000 to get kWh/Mo

  34. Go Green In Your Home Says:

    If you are only producing 90W and you need 1800W you will either need to charge many many batteries for a long time and only use them for a few minutes or you will need to get more solar panels. If you want an output of 1800W from an inverter, then you will need to generate a little more than 1800W as the inverter itself will use some watts to increase the voltage from 12VDC to 230VAC.

  35. Dhaval Says:

    I have a 01 number of solar module of 90W and I want output of 1800W, 230V AC from inverter. Is it possible? And if possible then, I should choose the battery of what rating? What should I keep in mind while choosing inverter?

  36. Teresa Says:

    The ultimate result would be to only have to input my monthly usage information over a 12month period and have the calculator/spreadsheet compare All the power company plans for my zipcode, which are numerous. View to see how many companies and plans are out there.
    We have to keep re-evaluating plans and contracts after they expire, with frequency depending on which plan we choose (variable, 12mo. fixed, etc.). I am looking to compare the most plans available with the least amount of effort. There are numerous variables to consider that make this task frustrating if not impossible.

  37. Go Green In Your Home Says:

    Do you want a spreadsheet that already has power company’s information in it or do you want to have a spreadsheet that has all the formulas and calculations already and you just enter information for each power company?

  38. Teresa Says:

    I have been searching for a spreadsheet that helps to determine what is the best power company to select based on residential usage. I have my monthly kWh usage for a couple of years. A few months are below 500kWh and most are below 1000 kWh for the year in the Houston area. We never reach 2000 kWh/mo. Folks are penalized for saving energy, because we are charged monthly fees for staying below the power company’s benchmark kWh number which ranges from 500 to 800 to 1000. Does someone know of a spreadsheet on the web (preferably free or inexpensive) that we can use when we are comparing the Facts Labels of the power companies? thanks.

  39. Go Green In Your Home Says:

    685kWh x $0.12/kWh = $82.20

  40. lama Says:

    prevoius reading-2897,
    present reading -3927
    the rate in kwh above 685-rs5/-& 690-rs10
    how much bill it come in a month

  41. Go Green In Your Home Says:

    What is your kWh usage normally on your bills?

  42. rich Says:

    If i get ui to put in net meter. and run my 60k generator. for how many hrs./days? my bill runs 6-800 per month @ .20 a watt i think (ct.) How long to get my bill to zero? Thanks esp. if you can figure what i’m looking for.

  43. Go Green In Your Home Says:

    Wow, I didn’t know that, that is crazy! I don’t know if you live in a rural area but if you did I’d toss up a wind turbine anyway! Also here I don’t think we need permits unless you are building a large tower for the wind turbine or if you put in new electrical circuits in breaker box. If we use a pole as tower and install turbine onto existing circuits I don’t think we need permits. I may be wrong though.

    Do you at least get a reason as to why you were denied installing a wind turbine or do they just say denied done and over with? You would think your government would want people to save some money and also save the environment. I don’t know how your electric is run there, but do you have different electric companies or does government control electricity? I know in Canada the government controls their water. Sometimes they get set on certain hours they are allowed to shower and do laundry. If you are not able to take a shower or do laundry in those hours too bad. Didn’t know if your electric was kind of like their water where government controls the electric or not.

    I guess the best you can do is follow the tips on this site to use less electric and try not to waste any at all, until you can find a way to generate your own electricity or at least a part of your electricity. Maybe a couple solar panels will at least save you some money even if you can’t power your entire home with them. Best of luck to you!

  44. Lee Says:


    we can’t use gas because it’s more expensive than electricity

    we can’t use generators because fuel is astronomical in price

    we can’t erect any sort of wind turbine because you need planning permission which is always denied.

    the only option we have is solar power, but of course here the sun hardly ever comes out lol

  45. Lee Says:

    I can’t believe how cheap electricity is for you Americans. Here in Britain I pay around £260 ($380) per month for my electric and I live in a 1 bed flat, that excludes water heating.

    My kilowat hour charge is 21 pence an hour.

    Electric is so expensive that most people just sit in cold houses because they can’t afford to run heating, not even in 1 room.

    If the government don’t do something about the costs I can see people going back to cutting down trees and burning them.

    The electricity companies increased the prices 3 times per year last year.

  46. Go Green In Your Home Says:

    5Aamps x 220Volts = 1,100 watts
    1,100watts x 12hours = 13,200watt hours
    13,200watt hours / 1,000watts = 13.2kWh
    13.2kWh x $0.10 = $1.32 to operate your device for 12 hours.
    You can also use our kWh calculator to calculate your kWh and cost. Just enter the values and it will calculate for you.

  47. stallone Says:

    An electric appliance takes 5A, When operated on a 220v supplied. Find the cost of operating of a appliance for 12 hours at 10kw/h.

  48. Go Green In Your Home Says:

    The 135wh/load can not be used to calculate the answer you are looking for unless you are storing electricity in batteries as well. Anyways, what you would need is the wattage rating on the washing machine. 600watt? etc. As long as the wattage on the machine does not exceed 3,000watts you will be fine. I highly doubt a washing machine will exceed 3,000watts. Dryer maybe, but not a washing machine. Your washing machine may not specify watts and may have voltage and amperage. If so just multiply the 2 together. 120VAC x 5amp = 600watts

    Hope this helps you!

  49. Barb Says:

    I know that an appliance ( electric washing machine ) uses 135 wh/ load. We have a 3000 watt generator. Can our generator handle this load?

  50. Calculater to Calculate Kwh | Go Green in Your Home Says:

    […] kWh usage you can use this kWh calculator below to calculate kWh. This calculator uses the same kWh formula found on Formula for kWh […]

  51. alz Says:

    and i find my ipad saves alot because i don’t need the lights to read also don’t need the house sound system on.cheers all!

  52. alz Says:

    hey i live off grid and hve for ten years or so.i live this but am really pleased there are some smart people out there helping the cause and don’t even know it.
    thanks for the discourse

  53. Go Green In Your Home Says:

    A battery bank wouldn’t help with the amount of panels and watts they generate. For the batteries to work you have to have excess watts that you are not using to charge them. Your batteries would never get charged, they would be constantly drained.

    Solar panels are good as they require almost no maintenance and last almost forever. Wind generators can produce more power for the money. They generate electricity even in the dark as long as you have wind.

    If you average is 1200kWh/mo you would need to roughly 2,000watts generated 24/7. Which at 90% efficiency (inveter on or off grid) would be 1,315kWh generated every month. Now if you have sufficient winds 24/7 a 2,000watt wind generator would be great. My guess is that you may not have sufficient winds 24/7 so may want to go slightly higher. Or make up some of the extra power needed with solar panels.

  54. Matt Says:

    would you maybe recomend that i make a wind turbine?

  55. Matt Says:

    Or larger panels. The instructions for the panels I am making say they should create 75 watts ea. However I was told by one of my local electric bike guys who deal with this type of energy often, that they would probably only generate about 45 watts and after reading these posts I assumed a 46 watt panel was what I was making. I am located in Michigan. so the average hours per day is only around 4. and I called my electric company yesterday and found out that my ave. mo. Kwh is 1200. Which peaks in aug at 2000 Kwh but for the most part around 800Kwh for about 3/4 of the year. But you would not suggest a battery bank for my situation? Also I have heard that grid tie inverters may not be safe (fire hazards). Also what size grid tie inverter would be appropriate? Sorry for so many questions but I am enthusiastic about going green (even if it is only a little bit).

  56. Go Green In Your Home Says:

    Your kWh would be printed on your electric bill. If you build 10 (46 watt) panels, that’s 460watts generated for 6 hours of sunlight (roughly as I don’t know where you are located). This will generate 2,760watts/day, 1,008,090watts/year. 84,007.5watts/mo. with a average inverter 90% efficiency, leaves you with 75,606.75watts/mo. or 75.60675kWh/mo. So you may want to either build more panels, or use a grid tie inverter instead.

    Basically a grid tie inverter you don’t use batteries, it ties into your electric company you currently have. You draw power from your panels when they are producing power, if they don’t have enough current or are not producing at night you will draw power from electric company. So it will basically drop your electric bill because you won’t pay for the power your panels produce, only pay for what you draw from power company.

    If my calculations are correct the 460watts of solar panels will drop your bill roughly $10 – $15/mo.

  57. Go Green In Your Home Says:

    Sorry, but I can’t calculate this as I don’t know what your utility company charges for transmission, kWh, extra fees, etc. Your electric bill will show kWh readings right on it.

  58. Matt Says:

    If you could suggest a formula for say 1000kwh per month for battery storage and inverter.

  59. Matt Says:

    Great Site!! I am currently building my own solar panels and have no problem doing so.
    Where my problem lies is in how many storage batteries and what type of inverter I will need.I have not rtied to calculate my kwH but we do use a lot of energy. A family of 6 with 3 computers a fridge and a deep freezer. I am planning on building about 8-9 (46 watt)solar panels.
    Also , most of the inverters I have looked at have 2 outlet plugs. How do I connect that to my house?

  60. zeth Says:

    what if our power bill cost 1, 500.oo, how can we get it’s kwh and what is the answer? hehe

  61. Patrick Says:

    and PS thanks for the great web site and feed back it really helps this old sailor

  62. Patrick Says:

    Hello again, I am looking for how to do the quantities. I was a carpenter in the seabees and I am an over-builder by design. “Better to have a little too much board then to cut it short cause there aint no board stretchers!” As far as panel storage I want to see if I can actually integrate them into the house itself. I am currently active on e-bay trying to get all the right stuff to pick up the next time I visit the family. B quality is good to go or are they all BS’ing me?

  63. Go Green In Your Home Says:

    Sounds great! Not sure what you are wanting. Do you want info on how many panels, batteries, and inverters will be needed or are you looking for more of design of panel storage? Like roof top and such?

  64. Patrick Says:

    Hi I am planning on building myself a home next year about 100 miles north of Rio De Janero. There is just two of use with our three dogs and our current usage is 500 KWH (high end). So I want to do an off-grid Solar power system with batteries. While I understand just a little about solar power I understand nothing about wind power systems). The house will be 110 power. Where do I look for a system design so I can build my home around it.
    PS will have two AC units, but no kids or rock concerts.

  65. Go Green In Your Home Says:

    I’m not 100% sure on this, as this will be working with real time figures instead of solid figures for an entire hour. I’m thinking you have voltage sensor (volt meter) and amperage sensor (ammeter). So you’re going to log these values to a computer automatically every 10 seconds I’m assuming?

    Well I would say for a more accurate real-time calculation you will want to use math function average for your voltage and for amperage, then use kWh formula plugging in the calculated averages. So if you take readings every 10sec that is 6 readings a minute, 360 readings an hour, and 8,640 readings a day. So you will take all 8640 readings for voltage add them together to get a sum, then divide by 8640 to get average voltage. Now do same with amperage to get average amps. Now convert the volts and amps to watts, (volt*amp=watts). Now that you have watts you will multiply by hours (which is 1) so your number will still be the same now divide by 1,000 to get kWh. Then you may do the same with output.

    We are using 1 hour even though all the samples were taken over a period of 24 hours because we already averaged the 24 hour period down to 1 hour. So that will tell you what your solar panels are producing and what you are using. You could also get a kWh meter, like electric companies use, well 2 of them, 1 for inputs and 1 for output.

  66. Tom Speller Says:


    I whould like to know how much power my solar system produces each day and how much I have used.

    I have a voltage and current sensors on both inputs and outputs but I can’t work out how to get a the kwh for a day.

    I plan to sample the current and voltage ever 5-10 seconds and calulate the watts it how to convert that into Wh or Wmins I strugeling with.

    Can you help.


  67. Go Green In Your Home Says:

    Okay so you are wanting to do a grid tie solar system, basically you pull electric from your solar panels as much as possible. Even if the panels are getting half sunlight and putting out half the watts, your home will use that half from the panels and the other half from power company. So first you will need your solar panels and a grid tie inverter. The panels feed direct current (DC) into the inverter. The inverter then converts the DC power to 120V alternating current (AC), which is what your home uses. The inverter also is fed 120VAC from your power company. If the power is available from solar panels it will consume it, if power isn’t sufficient, the inverter will make up for it from electric company.

    So few things before we get to the math, inverters have an efficiency rating just like everything else electrical. If the inverter is only 50% efficient you give it 100watt solar panel you only get 50watts. So you will want to factor that in as well.

    Another thing to consider is, how many solar panels do you want? Do you want enough to just power you through the daytime or do you want to have enough to power you through the night as well? You can get more solar panels than you need. Any extra watts you don’t use, goes to electric company, at end of month if you’ve given them the same as you used your free. If you are short, you pay them as normal, if you are over, they pay you! Example, you generate 1000kWh in a given month during daylight hours, you consumed only 500kWh in daytime, so at night you have 500kWh left, if you use 400kWh at night, electric company pays you for 100kWh. So you kind of use electric company as batteries. Another example, you generate 1000kWh in daytime hours from your panels, consume 700kWh in daytime, then consume 500kWh at night, thats 1200kWh you have used, but your panels only generated 1000kWh so you pay electric company for using 200kWh that month.

    So 6500watts is your maximum pull at a given time, you would use:
    Watts-Used / ( panel-watts x inverter efficiency ) = panels needed
    I would recommend looking at your current electric bill and looking for your kWh usage and not your maximum watts. Maximum watts really are only good for calculating off grid wind+solar hybrid systems, no battery storage accurately. Calculating grid tie or battery storage systems, you want to know your kWh to get an accurate calculation.

    Let me know what your kWh usage on your electric bill is and I can help you get a more accurate calculation for what you want. This way I can tell you how many panels you need if you want to cover just daylight usage, or daylight and nighttime, or even daytime, nighttime, and make $100/mo. from electric company. Whichever you want to do.

  68. Jigs Says:

    Yeah 6500Watt is my total home load including all my electrical appliances. This is a maximum load of my house, and the load is remain constant all the time, like i want to use the electrical power directly from sunlight, i don’t want to stored it in batteries.
    Like in night time or when there is no sunlight than i will use the supply of my local electric grid station.
    The system which i want to design is a Hybrid system, Like i want the electrical supply from solar panels and as well as from my local area grid station.
    If i have a panel available of 46 watt. than how many panels is required to hook up a load of 6500Watt, Only for 5 too 8 hours in day time. after that i switch it up to electric grid.

  69. Go Green In Your Home Says:

    Okay, well both have some right and wrong in them. There are a few missing variables though. Is this 6500watts going to be powered solely by solar panels? Is this system going to be on or off grid? The 6500watt you state, is this what all devices in your house add up to? Like TV 250watts, laptop 90watt = 340watts? or is this something on your electric bill? You will need to figure in hours of use to get kWh. You also are not going to generate 46watts from those panels for 14hours everyday. Look at solar insolation maps. They will tell you how many hours of sunlight you will get in a certain month in a certain location.

  70. Jigs Says:

    My home load is 6500watt, and one of the company have a panel rating of 46watt per module. than how much panel is required to hook up a load of 6500watt?
    I solve it in two methods? kindly you tell me which is right or wrong?

    According to my calculation:
    6500(load)*30.41(Days in a month)= 197.665kw
    *(My load is remain constant all the time)

    And the output of 46watt solar Panel (in 14 Hours of Sunlight daily) per month is= 46watt*14Hours*30.41Days= 19.58kwh per month.

    Total panel Required= 197.665kw/19.58kwh= 11 Panels of 46 Watt is Required


    or: 6500watt(home load)/46watt(one solar panel Rating)= 142 Panels is Required

    Is this calculation right or wrong?

    I shall be very thankful to you if you tell me the right thing?

  71. Go Green In Your Home Says:

    I would think you would generate electricity for more than 2 hours. I’m not sure what area you are in, but there are maps that show the hours per day you can generate electricity from solar panels. They are called solar insolation maps. You can search google for your area and see how many hours your panels can generate electricity. Most of these maps will also show you the solar insolation for different months throughout the year. Hope this helps! Thanks for stopping by.

  72. Paulette Says:

    Hi there, we use 16kw a day and are getting 240w monocrystalline panels. We were told to calculate on only 2 hours a day on average to get full 240w from each panel ie 480w max a panel each day in place in NZ that has the most sunshine hours in NZ. So 33 panels – these are big panels, dont know if the roof would be big enough – is 480w max right for a 240w panel per day?

  73. Najam Says:

    this is a good site. Just reading the articles and questions, I learned quite a bit.

  74. Go Green In Your Home Says:

    You are on track but you forgot a variable in your formula/calculation. Solar panels will not produce electric 24hours a day. They will only produce electric during direct sunlight hours. Also you will need a little more to account for surges. A home using 6kWh a day will not use 250watt constantly, they may use 1,000watts at once then 100watts on regular basis.

  75. Alfred Says:

    For the gentleman who consumes 6kwh per day, if a day has 24 hours, it means the wattage of the equipment=6000kwh/24. =250watts. so he needs 250/46 panels which is equal to approx. 6 panels.

  76. Go Green In Your Home Says:

    No, if you are wanting to calculate the amount of power you just follow the example above. Using that formula is how you calculate the kWh. A 60 watt light bulb draws 60 watts constantly, from turning on until you turn it off. Well there is some varying as far as turn on surge, peak, and rms, but the bulb is still pulling 60 watts. It doesn’t take an additional 60 watts to turn it on. Hope that answers your question.

  77. radhakrishna Says:

    if a 60w bulb draws 60w during switching on for i hour is it to be multiplied by 60*60 for 1 hour power calculation?

  78. Go Green In Your Home Says:

    Chris Dunne,
    You can measure each device yourself to figure out your kwh. As far as electric company it is measured on demand/in real time and added to your total. As soon as you turn on an electrical device your electric meter will move faster adding the electricity that device is using to the electricity the rest of the devices are using.

  79. Go Green In Your Home Says:

    r forfar,
    No, if you have 45amp service thats your peak. Whatever the breakers are rated at that is when they will trip. If a breaker is rated at 20amp you can’t pull more than 20amps from that breaker at once, over time don’t matter. Which is 2,400watts. So if you have a device like AC, oven, something that pulls more than 2,400watts, then that breaker will trip and need reset.

  80. Chris Dunne Says:

    Hi, Good info on this site, all the calculatios are based on a constant load over time. What if the load is variable (many and various loads). If the kwh meter was an old spinning disk type then the disk will speed up and slow down accordingly, with a digital system how many samples should I take, I’m guessing per second. Is there some kind of standard that states sampling rate of digital systems meauring watts over time to creat kwh.

  81. r forfar Says:

    Given 3 breakers (45 amp service) could I use 15.5 KWH of electricity a day without blowing the breakers? I’m in a shared bill situation (20%) which seems to be too high for my 3 breakers. Thanks, Russ.

  82. Go Green In Your Home Says:

    2,000kwh/mo. is averaging 65.8kwh/day, so you would need to be able to generate about 3kw but you will also loose some power in your inverter. Depending on the efficiency of the inverter you would probably want around 5kw wind generator as well as battery bank for storing. If using solar panels you will want almost 3 times the amount as you are only going to be generating power for around 8hours a day. If using a gas generator 120vac with no battery bank you will need to figure out what the most watts used at a single time is, not what you average a month.

  83. Go Green In Your Home Says:

    You could also use wind power or solar power. I would recommend wind power with battery banks as it is cheaper as well as constant. I will soon be adding a few articles on wind and solar energy. How to figure out what size you need, how to setup or install everything, etc.

  84. Go Green In Your Home Says:

    120VAC x 4A = 480watts
    480watts x 24hours x 365.25days / 1000watts / 12months =350.64kwh per month

  85. Eric Pintar Says:

    Dear Sir,
    I am a little confused with so many units. I want to power my house with solar panels or gas generator b ut don’t know where to start. I calculated the average monthly use of electricity and it’s 2,000KWh ( two thousand kilowatt hour per month ).
    It’s a 4,000sf house with 2 ac units.

    I appreciate your help.
    Tks, Eric

  86. Dino Says:

    Hey, Great site you have here!

    I am in the midst of setting up a commercial, urban farm in an old warehouse, using LED light technology to act as the sun. I am currently in the restaurant business, and thanks to your site I figure I will look into getting a high end diesel electric generator, use my restaurants cooking grease (refine it) and use it to power up the warehouse. I will do some number crunching.. thank-you!!

  87. Dr Shahid Mahmood Says:

    Very good site

  88. Bob Says:

    I am having trouble trying to accurately figure out how many KWH a machine is using and could use some help. It is 4 amps, the AC input is a regular household plug (100-240)

    I keep coming up with 4 amps at 100volts = 4kwh

    At 24 hours a day that is 96KWH per day and at 30.5 days a month that is 2,928 kwh per month

    It seems high to me???

  89. Go Green In Your Home Says:

    This depends if you are going to store electric as well. If you are not going to store electric, you need to find out the max wattage you use at a time, regardless of long term. So basically if you are measuring kWh with a meter or something you need to turn on all devices in your home that would normally be on at the same time. If this equals out to 3kW, then your solar + wind need to be combined to atleast 3kW. Maybe 2kW wind generator and 1kW of solar panels.

    Now if you are going to store electric in batteries then you need to know your combined usage in a month rather than your peak usage at a single instance. Then your panels and wind generator need to make this amount in the month. Example, if the most I’ve used in any given month is 280kWh, so 280kWh x 1,000 = 280,000watts / 30.5 days / 24hours = 382.513661202watts per hour. So I could get away with using a wind generator that produces 400watts rms.

    If your max usage a month is 2007kWh and you are going to be storing electric, 2007kWh * 1,000 watts = 2,007,000watts / 30.5days / 24 hours = 2741.803278689 or (2.741803279 kW). So you would need to produce around 3kW rms. I would recommend using a charge controller as well as a couple battery banks to store your electric in.

    Hope this helps, if you need any more help let me know.

  90. omar Says:

    Dear Sir,

    can you help me out with the following.
    i want to buy a wind and solar system but i don’t know of what amount i should buy. my house is using at the moment 2007khw/m.
    can you guide me in the right direction for the amount of wattage or kw equipment i should buy? where i live we have a perfect weather all year for both solar an wind systems.
    i would realy apreciate your help.

    Best regards,


  91. Malik Says:

    Dear Sir,

    Can you give me a rough idea, that this 100W can operate how many house hold appliance daily. e.g. Laptop, fan, lights and TV.

    Best regards.


  92. Malik Says:

    Dear Sir,

    Thank you very very much for your kind support and assistance. I got the answer quite up to my expectations. Thank you and God bless you.

    Best regards.


  93. Go Green In Your Home Says:

    Well this depends on what appliances you run in your home, as well as if you are going to have the electricity stored in batteries for when you are not using it directly. I don’t know for sure if you will get 1800W daily from this panel. If the panel is 100W it would have to have optimal sunlight for 18 hours to produce 1800W. There was a website that you type in where you are going to have your panel outside geographically and it tells you how many hours of sunlight you will get.

    A single 100W panel will only help reduce your electric bill, but not run totally on solar.

    In my area I can get 14 hours of sunlight in summer (middle of June)
    If this 100W panel was getting 14hrs of sunlight, 1400W a day x 365.25 / 1,000 = 511.35kWh x $0.1 = $51.135/year.

    This means if I have this 100W solar panel I would save $51.14 every year on my electric bill.

    If you are wanting to run 1 single device directly off of this you can run a laptop only. As most laptops consume around 90W. You may also be able to run a light, but if you are using standard lights, a 60W bulb would be all you can run. If you use LED or CFL bulbs, you can run a lot more. But without storing the electric, or using paired with an electricity service provider, that’s all you are going to run.

  94. Malik Says:

    Also i want to know what should be good amount to be spent on this device. I mean to say up to maximum what price i should take it (in US dollars) so kindly give me a rough idea.

    Best regards.


  95. Malik Says:

    Dear Sir,

    I am looking to buy a Solar system, they are claiming it’s size is

    100W: ø 14 cm, height 10 cm, weight 0.295 kg
    and producing
    100W produces an average of 1800W hours (1.8kW hours) daily. Can you guide me how many home appliances it can operate daily. is this a good device to take. I need your kind reply on urgent basis.

    I liked you efforts very much.

    Best regards.


  96. Go Green In Your Home Says:

    Lauren, you are very welcome. Glad my site could help you out with your homework. Hopefully you and your family can use some of the tips on here as wll to help save some money on your bills! Hope you get an A+

  97. Lauren Says:

    I love this site. It helped me with my homework. I am in 6th Grade, and we have a science project about saving energy, in our homes. i looked up how to measure kwh on And your wonderful site popped up. It made my day to had someone out there that actually knows about this stuff. I was clueless. But not any more. You made it so easy to understand.Once more I would love to thank you guys for all your hard work, of putting this site together. Keep up the good work.

  98. Go Green In Your Home Says:

    110volt x 63amps = 6,930watts
    So now you have the watts, plug the watts into the formula in the information above to figure out kwh. You need to know how long this runs for. 6,930watts x runtime hours / 1,000 = kwh
    to get runtime hours you can do hours x days = runtime hours.
    So if this device ran for 8hours everyday… 8 x 365.25 = 2,922 runtime hours a year.
    Now we plug that into the formula… 6,930watts x 2,922runtime hours / 1,000 = 20,249.46kwh a year or.. divide by 12 to get monthly… 20,249.46 / 12 = 1,687.455kwh every month

  99. RLK Says:

    How can we calculate the KWH if we know the 63 amp, 110volt, 50 Hz this much date

  100. Go Green In Your Home Says:

    If you are talking about a electric generator with a diesel powered engine, they should have the rms watts it produces and how many hours it will run on a tank of fuel. So if you get a generator that is 2,800 watts, 4 gallon tank, and runs 8 hours. You can generate 2,800 watts x 5 hours / 1,000 = 14kWh so it takes 4 gallons of fuel to generate 14kWh. So 4 gallons x $3.30 per gallon of fuel = $13.20 to generate 14kWh, so $13.20 / 14 = $0.94285714 per kWh. So $0.95 per kWh.

  101. muthukumar Says:

    how can be check the duesel engine efficience and cos of units

  102. Go Green In Your Home Says:

    Well I also need the voltage, but I’m going to assume this is 120VAC. So to figure out watts we would do Volts X Amps = Watts So 120V x 2.7A = 324W Now that we have the watts, we need watthours. Which we would do Watts x Hours = watthours.. But you run 24/7 so we will figure out yearly then drop to monthly.. 24hours x 365.25days = 8,766 hours a year.. so watts x hours = watthours, 324W x 8,766hours = 2,840,184 watthours a year. we want kWh though so lets divide by 1,000.. 2,840,184 / 1,000 = 2,840.184kWh per year.. at $0.10 per kWh thats 2,840.184kWh x $.1 = $284.0184 per year..

    Now for monthly we want to divide by 12, since their is 12 months.. 284.0184 / 12 = $23.6682 per month.

    But this will be high amount as this is if the pump ran 24/7, which I doubt it does, I’m sure the pump shuts off every now and then when it’s not pumping water, unless this is a water fountain or something. Hope this helps.

  103. aidy Says:

    i have a water pump thats running at 2.7 amps and runs for 24 hours a day could you tell me how many electrical units it takes every day thanks in advance aidy

  104. Go Green In Your Home Says:

    So your household consumes 10kwh, is this 10kwh per month? per day? If you consume 10kwh per month and you pay $1.80 per kwh, then your cost is $18/mo. If you consume 10kwh each day, then 10kwh x 1.8 x 365.25 / 12 = $547.875, which electric company would then round up to $547.88

  105. naveen Says:

    i still didnt get how to solve this sum “If a electricity consumption of your house is 10 kwh and the rate of electricity is 1.80 per unit, find for how much you have to pay for consumption in 30 days?

  106. David Says:

    Your method of calculating kwh will get you close. To get true kwh you must first convert watts to jules and then convert jules to kwh. This is done by multiplying watts by 3.6X1000000. This number is then multiplied by 2.75X 10 to the negative 7th power (sorry, I don’t know how to show exponents). The simplified method shown will be conservative, but there is nothing wrong with that!

  107. Go Green In Your Home Says:

    Thanks, glad to hear my site has helped you solve your problem!

  108. Edwin M Says:

    Agradesere en el alma su valiosa publicacion
    respetado autor me ayudo a solucionar una aplicacion
    complicadisima la cual tenia en ahorro de energia.
    hasta pronto.
    saludos fraternales desde BOGOTA COLOMBIA.

  109. michael Says:

    it made me learn something valuable, thankyou.

  110. Go Green In Your Home Says:

    You may want to send me a file, may help me understand what you are looking for easier. Also the Hubbell plug you can buy on amazon cheaper. Hubbell HBL5466C Plug. You can send an email to if you want to send the file to me.

  111. Go Green In Your Home Says:

    I created an MS Excel file for you, that you can use. Electric Usage Spreadsheet. Hope this helps you!

  112. Bob Says:

    How would one write an MS Excel formula for this, given that:

    Total Wattage is known in cell D8
    Wattage is used 24 hours per day
    kWh to be displayed in cell E10



  113. Dan Ambroise Says:

    Hydro Electricity Rates under TOU – Spring 2011

    How will I be affected by the change in the way that hydro useage will billed for the
    heating of my hot water tank?
    $/kWH #/hrs/weekday weekends weekly hours %/week
    Off peak rate $0.053 10 24 98 58.33333333
    Mid peak rate $0.080 8 0 40 23.80952381
    On peak rate $0.099 6 0 30 17.85714286
    Total 168 100%

    So what are the costs of heating your water depending on whether or not you can control it’s on time? Is it worth your while to invest in the modification? What is the ROI (return on investment)?
    How much is the cost of the modification to the hot water heater electrical system to be able to control when my heater turns on during off peak hours only?
    cost of materials
    timer HB114C $16.50
    plug HBL5466C $27.18
    recept HBL5461C $24.28
    labour $60.00
    total $127.96

    At what point (after how many hours) will I make that money back if I do the modification?
    8700 hrs random on 58.3% of time at off peak $268.98
    28.3% of time at mid peak $165.71
    17.8% of time at on peak $153.80
    Total cost of 900 hrs $588.49
    8700 off peak hrs only 100% of time at off peak $461.10
    Savings $127.39
    Conclusion: Around the 8700 hour mark, the ROI is reached.

    Just how much hot water do I have to use to reach 8700 hours of use?
    That will depend on
    1)How much hot water that you use on a weekly/monthly basis; laundry, dishes, bathing
    2)The temperature of the water coming into the tank, (several degrees lower in winter)
    3)The set point temperature that the tank has been set to turn on
    4)The efficiency of the tank to minimize heat loss through convection/conduction of heat

    Although these are measureable quantities, I will make some assumptions instead.
    1)That I use 400 litres of hot water in a month.
    2)That the average temprature of the incoming water is 50 degrees F.
    3)That the tank is going to heat and keep the temprature at 140 degrees F.
    4)That the efficiency of the tank is 100%, as if that were even possible.

    One British Thermal Unit (BTU) is the amount of energy to raise 1 pound of water by 1 degree F.
    400 litres of water weighs 881.6 pounds
    The difference between 140 deg. F. 50 deg. F.
    90 deg. F.
    Amount of energy req. 79344 BTU
    3413 BTU equals 1 kWH
    23.24758277 kWH

    This doesn’t look as prety as my excel sheet. Can I send you an attachment.
    I need help figuring the ROI and wondered if you could help

  114. Go Green In Your Home Says:

    Watt x 1 hour/day x days / 1,000 = kWh
    then multiply kWh by cost per kWh to find cost.

    so if this was a 60watt bulb..on 1 hour every day of the year…
    60 watt x 1 hour x 365.25 days/year / 1,000 = 21.915 kWh

    now if you pay $0.10/kWh now we do:
    21.915 kWh x 0.10 = $2.19 / year

  115. Go Green In Your Home Says:

    (100 watt bulb x 6 hrs/day x 30 days) x 6 bulbs / 1,000 = 108 kWh .. now I’m not sure what rs or 2.00/unit is for.. but take the 108 kWh and multiply it by how much your electric company charges you per kWh.

  116. Go Green In Your Home Says:

    This really depends.. the kWh per day doesn’t really matter too much when you are trying to calculate how much power you need. The other variable you will need to know is the maximum you consume at once. Say an A/C unit will draw 3,500 watts at a time, if that and your electric oven ( 3,000 watts ) turn on at the same time, that’s a current draw of 6,500 watts at one time. So you would need enough solar panels to supply 6,500 watts at once ( 6,500 watts usage / 46 watt solar panel = 141.304347826 ), so you would need 142 solar panels that produce 46 watts.. which is ridiculous. So you need a way to store this power, when you aren’t using it. To store the power you would need a charge controller and a battery bank. Well 6 kWh /day would be 182.625 kWh / month. I’ll give you a little more just incase. So 7 kWh /day will give you 213.0625 kWh / month. ( 7 x 365.25 / 12 = 213.0625 )… Now a single 46 watt solar panel can produce ( 46 watt x 14 hrs of sunlight x 365.25 days a year / 12 months / 1,000 = 19.60175 kWh / month ) you need to get 213.0625 kWh just to be safe, so 213.0625 kWh needed / 19.60175 kWh per panel = 10.869565217.. so 10 – 11 solar panels would work fine for you. You can get some solar panels online that can produce more watts so you don’t need as many. But sometimes a lot of smaller panels might be cheaper.

  117. karthik Says:

    hello sir,
    i am using watt meter lamp used 1 hour per day . how to calculate kwh..? please reply


    a bulb of 100w is blown 6hrs/day .at a time we have blown 6nos for 30days.what would be the charges will be taken at rate of rs 2.00 /unit?please send the answar…

  119. Victor Says:

    I consume an average of 6 kWh per day. A solar panel supplier is offering me panels of 46 watts and 34 watts each. How many panels do I need to supply the consumption I have and be sure I will not run out of electricity at any time?

  120. Go Green In Your Home Says:

    Wow, 8.5KW?? That’s 8,500 watts? Well if that figure is correct, and it is on for 5 hours a day, that would be 8,500 x 5 = 42,500watt hours, which then you would convert this to KWH, 42,500 / 1,000 = 42.5KWH / day the device is in use.. at $0.10/KWH that would cost you, 42.5KWH x $0.10 = $4.25/day or $4.25 x 365.25 days = $1,552.31/year!

  121. Santosh Says:

    8.5KW*5Hrs/day how much KWH unit?

  122. Alberto Says:

    What kind of device (KW or KVA)you recommend for supply 14,025 Kwh/month?

  123. Go Green In Your Home Says:

    Yes, you can do that, as long as you link back to this site. Hope you find our information very helpful and come back to find more and more information on how to go green and save money!

  124. Polprav Says:

    Hello from Russia!
    Can I quote a post in your blog with the link to you?

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