Convert kWh to J kilowatt hours ↔ joules Free Online Secure
Type a value in kilowatt hours and read it in joules at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert kWh to J (kilowatt hours ↔ joules)
| kWh | J |
|---|---|
| 1 | 3600000 |
| 2 | 7200000 |
| 3 | 10800000 |
| 5 | 18000000 |
| 10 | 36000000 |
| 20 | 72000000 |
| 50 | 180000000 |
| 100 | 360000000 |
Where these units come from
Energy collected a unit from every field that discovered it separately. The joule is the SI one and the plainest: a newton acting over a metre. The calorie came from the study of heat and was defined by warming water one degree — which is why there are several of them, depending on which degree you start from; the thermochemical calorie, exactly 4.184 J, is the one used here. The kilowatt hour is not a physicist's unit at all but an accountant's: a kilowatt drawn for an hour, which is how electricity is sold. The BTU is its British cousin, built from the pound and the Fahrenheit degree, and it still runs the heating and cooling trade worldwide.
Where you meet them
Joules belong to physics and to food labels outside the English-speaking world. Kilowatt hours arrive on every electricity bill and describe the capacity of batteries, from a phone to a car. BTUs rate air conditioners, boilers and gas appliances almost everywhere, including in countries that are otherwise entirely metric. Calories — in practice kilocalories — rule nutrition, which is the one place where the unit's name is routinely a thousand times out.
Questions people ask
Why is a kilowatt hour not just a kilowatt?
Because one is a rate and the other is an amount. A kilowatt is how fast energy flows — a kettle draws about two of them. A kilowatt hour is what you get if that flow continues for an hour, and it is what the meter counts and the bill charges for. Running a 2 kW kettle for six minutes uses 0.2 kWh; running a 10 W lamp all day uses about the same.
What is a joule in everyday terms?
A joule is about the energy needed to lift a small apple, around 100 grams, by one metre. It is also the energy of one watt flowing for one second, and one newton moving something one metre. It is a small unit, which is why household energy is counted in kilojoules, megajoules or kilowatt hours.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Kilowatt-hours to joules: grid storage, electric transport and heavy industry
Electricity is sold by the kilowatt-hour, but a physicist, a battery designer or a grid planner has to compare it with fuel, with falling water and with chemical reactions, and those are all counted in joules. A home battery of 13.5 kWh, a pumped-storage plant of 9 GWh and a steelworks' annual use all land on the same scale once converted. To convert kWh to J, multiply by 3,600,000: 1 kWh is 3.6 MJ, 60 kWh is 216 MJ and 1 MWh is 3.6 GJ. The calculator above multiplies as you type, and the sections below take you from a car battery to a national grid.
The page gives the rule with worked examples, a profile of each unit, a comparison and a long run of examples from storage, transport and industry, followed by the usual mistakes. The calculation runs in your browser and nothing you type is sent anywhere. For billing, always rely on your meter and your supplier.
How to convert kWh to J: multiply by 3,600,000
The rule
A kilowatt-hour is the energy used by a 1,000 W load running for an hour: 1,000 W × 3,600 s = 3,600,000 J. To convert kWh to J, multiply the kilowatt-hours by 3,600,000. 0.5 kWh gives 1,800,000 J, 7.5 kWh gives 27,000,000 J and 100 kWh gives 360,000,000 J. To go back, divide joules by 3,600,000.
Worked examples
An electric kettle heating a litre of water uses 0.093 kWh, which is 334,800 J. A dishwasher cycle of 1 kWh is 3.6 MJ. A phone battery of 15 Wh, or 0.015 kWh, holds 54,000 J.
An exact factor
The number comes straight from the definitions of the hour and the watt, so it carries no rounding. The only difficulty is the number of zeros, which is why MJ, GJ and TJ are used.
A quick sanity test
The answer in joules is 3.6 million times the number of kWh. If a “convert kWh to J” calculation gave a smaller number than you started with, you divided instead of multiplying.
The kilowatt-hour
The unit on the bill
The kilowatt-hour measures and prices electricity for homes, firms and grids. Your meter counts kWh, and the price is stated per kWh. It is also the unit in which batteries and storage plants are rated.
Where it appears
Electricity bills, battery specifications, grid statistics and appliance labels.
The joule
The SI unit of energy
The joule is the energy of one watt acting for one second. Every equation of physics that involves energy, from kinetic energy to the heat of reactions, yields joules, so a conversion from kWh is needed whenever bills meet formulas.
Where it appears
Physics, chemistry, engineering calculations and international standards.
kWh against joules
One kWh is 3,600,000 J, so the figure in joules is 3.6 million times larger. 0.1 kWh is 360,000 J, while 1,000 kWh is 3.6 billion joules, or 3.6 GJ. Both units measure the same energy; only the scale differs.
The conversion is exact and hides no rounding. The main trap is the number of zeros: one place too many or too few changes the result tenfold.
Where the conversion shows up
Home batteries and cars
A home battery of 13.5 kWh stores 48.6 MJ. A small electric car holds 40 kWh, 144 MJ, a family model 60 kWh, 216 MJ, and a long-range saloon 100 kWh, 360 MJ. A “convert kWh to J” calculation puts them on the same scale as a tank of fuel measured in megajoules.
Grid storage
A large battery plant of 194 MWh holds 698 GJ. A utility container battery of 3.9 MWh holds 14 GJ. Pumped-storage stations store far more: one with 9.1 GWh holds 32.8 TJ, and the largest, near 24 GWh, 86 TJ.
Heavy industry
Making a kilogram of aluminium takes about 14 kWh, 50 MJ, and a tonne of steel in an electric arc furnace about 400 kWh, 1.44 GJ. Desalinating a cubic metre of sea water needs about 3 kWh, 10.8 MJ.
Energy density of batteries
A lithium-ion cell stores about 250 Wh per kilogram, which is 900 kJ/kg. Petrol holds 12,000 Wh/kg, 43 MJ/kg, nearly fifty times more by weight. A “convert kWh to J” calculation reveals why a battery-powered aeroplane is so hard: 100 kWh of battery weighs 400 kg, while the same energy in fuel weighs 8 kg.
Fast chargers against fuel pumps
A fast charger of 150 kW delivers 150 kWh in an hour, so in 20 minutes it puts in 50 kWh, 180 MJ. A petrol pump flowing at 35 litres a minute moves 1.18 GJ a minute, equal to 19.7 MW. That is why the pump is so much faster than any charger, and why a “convert kWh to J” calculation on both makes the gap plain.
The magnets of the LHC
The superconducting magnets of the Large Hadron Collider store about 10.4 GJ of magnetic energy, which is 2,890 kWh, roughly a family's electricity for a year. The beam itself carries 362 MJ, 100 kWh. The magnets' energy has to be removed safely if a quench occurs.
Hurricanes
The heat released by condensation in a mature hurricane is of order 6 × 10¹⁴ W, which over a day is 5.2 × 10¹⁹ J, 1.4 × 10¹³ kWh. That is about half of the world's yearly electricity use, spent every day by the storm. Kilowatt-hours are seldom used for such numbers, joules are.
E-bikes
An electric bicycle battery of 0.5 kWh stores 1.8 MJ and carries a rider about 60 km. That is 30 kJ per kilometre, 8 Wh/km, a tenth of the energy per kilometre of a small electric car. A cyclist pedalling at 100 W for an hour adds 0.1 kWh, 360 kJ.
Standby and idle losses
Devices on standby drawing 5 W use 43.8 kWh a year, 158 MJ. A home with twenty such devices wastes 876 kWh, 3.2 GJ, over 12 months. Standby consumption is small per device but significant in a country with millions of homes.
Street lighting
A street lamp of 150 W burning 4,000 hours a year uses 600 kWh, 2.16 GJ. Replacing it with a 50 W LED saves 400 kWh, 1.44 GJ, a year. A city with 50,000 lamps would save 20 GWh, 72 TJ, on lighting.
The mental shortcut
When you need a “convert kWh to J” calculation on the back of an envelope, multiply by 3.6 and call the result megajoules. 2 kWh becomes 7.2 MJ, 15 kWh becomes 54 MJ, and 150 kWh becomes 540 MJ. For Wh, multiply by 3.6 and call it kilojoules.
Spreadsheet formulas
To convert kWh to J in a spreadsheet, put the energy in kWh in column A and type =A2*3600000 in column B. For the reverse, =B2/3600000. A column with =A2*3.6 gives megajoules, which keeps the results readable.
Rounding and precision
Household meters are accurate to 1 or 2 per cent. When you convert kWh to J for a bill, three digits are enough: 234 kWh is 842 MJ. Keeping every digit adds nothing to the information.
Landmarks to memorise
0.001 kWh is 3,600 J. 0.01 kWh is 36,000 J. 0.1 kWh is 360,000 J. 1 kWh is 3.6 MJ. 10 kWh is 36 MJ. 100 kWh is 360 MJ. 1,000 kWh is 3.6 GJ. Use these to convert kWh to J by eye.
Electric buses and trucks
An electric city bus carries 300 kWh, 1.08 GJ, and a long-haul electric truck 600 to 800 kWh, 2.2 to 2.9 GJ. A truck using 1.5 kWh per kilometre, 5.4 MJ/km, can cover 400 to 500 km on one charge before it needs a pause.
Reference ladder
0.05 kWh is 180,000 J. 0.3 kWh is 1.08 MJ. 3 kWh is 10.8 MJ. 24 kWh is 86.4 MJ. 200 kWh is 720 MJ. 500 kWh is 1.8 GJ. 2,500 kWh is 9 GJ. 5,000 kWh is 18 GJ. A table like this makes checks quick.
Checking by reversing
To check a “convert kWh to J” calculation result, divide the answer by 3,600,000. If 5 kWh became 18,000,000 J, dividing returns 5. A second test is size: the joule figure has six more digits.
Link to calories and BTU
One kWh is 860 kcal, 3,412 BTU and 3.6 MJ. Two kWh is 1,721 kcal, 6,824 BTU and 7.2 MJ. For comparisons with old or American documents, passing through MJ keeps the arithmetic safe.
A charging session in joules
A driver plugs in at 12 per cent and unplugs at 80 per cent of a 75 kWh battery, adding 51 kWh. In joules that is 51 × 3,600,000 = 183.6 MJ. At 100 kW the session lasts about 31 minutes. Dividing the energy by the time gives back the 100 kW, a useful check on a “convert kWh to J” calculation.
Peak and average power
A building may peak at 500 kW while using only 120 kW on average. In a day the average load uses 2,880 kWh, 10.4 GJ. Utilities charge for both the peak, in kW, and the energy, in kWh. The joule is nothing more than a watt-second, so both are covered.
Electric ferries
A large electric ferry carries a battery of about 4 MWh, 14.4 GJ, enough to cross a 20 km strait several times between charges. Charging takes 10 minutes at the quay with a megawatt-scale connection. Naval architects work in kWh and in MJ.
Humans as engines
A trained cyclist can sustain 250 W for an hour, 0.25 kWh or 900 kJ, while a well-fed adult takes in 8.4 MJ a day. Peak human output over a few seconds is above 1,500 W, but the energy is small: 1.5 kW for ten seconds is 15 kJ, only 0.004 kWh.
Two routes to one answer
You can go from kWh to joules directly with 3,600,000, or via MJ: multiply by 3.6 and then by 1,000,000. If the results disagree, a digit was copied wrongly.
Cryogenics and liquefied gas
Liquefying a kilogram of natural gas takes roughly 0.3 to 0.5 kWh, 1.1 to 1.8 MJ, and a kilogram of nitrogen about 0.4 kWh, 1.4 MJ. A plant making 10,000 tonnes of liquid nitrogen a year therefore uses 4 GWh, 14 TJ. Process engineers quote kWh per tonne, which suits the electricity bill.
Water pumping and supply
Lifting a cubic metre of water by 100 metres needs at least 981 kJ, 0.27 kWh, and real pumps use about 0.4 kWh because of losses. A town of 100,000 people using 150 litres each per day lifts 15,000 cubic metres, so the pumping bill is some 6,000 kWh, 21.6 GJ, a day, large enough to dominate a municipality's energy use and the reason water utilities invest so heavily in efficient pumps and in reducing leaks from old pipes.
Trains and trams
A high-speed train traveling at 300 km/h uses a power of around 8 to 10 MW. In an hour that is 8 to 10 MWh, 29 to 36 GJ. A modern tram uses 3 to 5 kWh per kilometre, 11 to 18 MJ/km. Railway operators report in kWh per passenger-kilometre.
Aircraft fuel
A long-haul airliner burns around 100 tonnes of fuel on a big sector, at 43 MJ/kg, which is 4.3 TJ, or 1.2 GWh. A battery to carry the same energy would weigh 4,800 tonnes at today's densities. The comparison explains the delay in electric long-distance flight.
Data centres
A data centre drawing 10 MW consumes 87,600 MWh in a year, 315 TJ. Large cloud sites use 100 MW or more, 3.15 PJ a year. Operators quote consumption in MWh and GWh, while a physicist would convert to joules to compare with other kinds of energy use.
Green hydrogen
Producing one kilogram of hydrogen by electrolysis takes about 50 kWh, 180 MJ, and the gas holds 120 MJ, 33.3 kWh, so the round trip has an efficiency of about two thirds. Turning it back into electricity in a fuel cell halves it again. These conversions explain why hydrogen is used for sectors that cannot be electrified directly.
Tidal barrages
The tidal power station on the Rance estuary, with 240 MW installed, delivers about 500 GWh a year, which is 1.8 PJ. Tide mills of this kind work in both directions. Their output is predictable to the minute, unlike wind, and is quoted in GWh by their operators.
Nuclear plants
A 700 MW reactor running a full day generates 16.8 GWh, 60.5 TJ. In a year at 90 per cent availability it generates 5.5 TWh, 19.9 PJ. The fuel needed is tens of tonnes of uranium, whose energy content in joules is vastly higher than that of coal for the same output.
Supercomputers
A leading supercomputer draws 20 to 30 MW. In a year that is 175,000 to 260,000 MWh, 630 to 950 TJ. Its operators care as much about the kilowatt-hours as about the speed, since the bill for electricity over five years can approach the purchase price.
More values for convert kWh to J
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 kWh = 360,000 J
- 0.5 kWh = 1,800,000 J
- 3 kWh = 10,800,000 J
- 4 kWh = 14,400,000 J
- 7 kWh = 25,200,000 J
- 15 kWh = 54,000,000 J
- 20 kWh = 72,000,000 J
- 75 kWh = 270,000,000 J
- 200 kWh = 720,000,000 J
- 500 kWh = 1,800,000,000 J
- 2,000 kWh = 7,200,000,000 J
- 10,000 kWh = 36,000,000,000 J
Common slips with a “convert kWh to J” calculation
Dividing by 3.6 million
From kWh to joules the number grows. If 5 kWh became 0.0000014, you divided instead of multiplying.
Confusing kW and kWh
The kilowatt is power, the kilowatt-hour is energy. A 2 kW appliance uses 2 kWh only if it runs for an hour. Read the unit on the label carefully.
Wh and kWh
A Wh is a thousand times smaller than a kWh. A phone battery of 15 Wh is 0.015 kWh, not 15 kWh. A slip of unit gives an energy a thousand times too large.
Short answers
How do I convert kWh to J?
Multiply the kWh by 3,600,000.
How many joules is 1 kWh?
Exactly 3,600,000 J.
How many joules is 10 kWh?
36,000,000 J, or 36 MJ.
How many kWh is a million joules?
0.278 kWh.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other energy conversions see Convert kWh to BTU, Convert kWh to cal, Convert cal to J, Convert J to cal, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert yd³ to m³. The reverse direction is Convert J to kWh.
In short, a “convert kWh to J” calculation comes down to multiplying by 3,600,000 and writing the unit beside the answer. Your number is computed locally, with no account and no upload.