Convert J to kWh joules ↔ kilowatt hours Free Online Secure
Type a value in joules and read it in kilowatt hours 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 J to kWh (joules ↔ kilowatt hours)
| J | kWh |
|---|---|
| 1 | 0.000000277777777778 |
| 2 | 0.000000555555555556 |
| 3 | 0.000000833333333333 |
| 5 | 0.00000138888888889 |
| 10 | 0.00000277777777778 |
| 20 | 0.00000555555555556 |
| 50 | 0.0000138888888889 |
| 100 | 0.0000277777777778 |
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
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.
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.
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.
Joules to kilowatt-hours: the tiny energies of sensors, flashes and heartbeats
Anyone who designs a pacemaker, a wireless sensor or a camera flash works in microjoules and joules, whereas the people who pay for batteries and power think in watt-hours and kilowatt-hours. The two worlds meet when someone asks how long a coin cell will last or what a billion sensors would cost to run. For a “convert J to kWh” calculation, divide by 3,600,000. One joule is 2.78 × 10⁻⁷ kWh, 3,600 J is 0.001 kWh and 36 MJ is 10 kWh. The calculator above divides while you type, and the sections below set figures from electronics and medicine on the kilowatt-hour scale.
Below you will find worked examples, a profile of each unit, a comparison, many cases of small-scale energy and the common slips. All computing happens in your browser. Battery life always depends on conditions, so treat estimates as a guide.
How to convert J to kWh: divide by 3,600,000
The rule
One kilowatt-hour is exactly 3,600,000 joules. To convert J to kWh, divide the joules by 3,600,000: 7,200,000 J gives 2 kWh, 180,000,000 J gives 50 kWh and 1.8 × 10¹² J gives 500,000 kWh. To go the other way, multiply kWh by 3,600,000.
Worked examples
A camera flash of 50 J equals 1.39 × 10⁻⁵ kWh. A defibrillator shock of 200 J equals 5.6 × 10⁻⁵ kWh. A coin cell holding 2,430 J contains 0.000675 kWh, which is 0.675 Wh.
An exact factor
The factor follows from the definitions of the hour and the watt and has no hidden rounding. For small energies it is easier to move to watt-hours first: 1 Wh is 3,600 J, and then divide by 1,000.
A quick sanity test
The answer in kWh is 3.6 million times smaller than the number of joules. If a “convert J to kWh” calculation gave a larger number than you started with, you multiplied instead of dividing.
The joule
The unit of engineers' budgets
The joule, one watt for one second, is the natural unit for the energy of a single event: a radio message, a heartbeat pulse, a flash. Datasheets for low-power electronics quote energy per operation in microjoules and millijoules.
Where it appears
Electronics datasheets, medical devices, physics and energy-harvesting studies.
The kilowatt-hour
The unit of the meter
The kilowatt-hour is how households and companies pay for electricity. It is huge compared with the energy of one electronic event, but it becomes a natural unit when the events are billions in number or the product is a large battery.
Where it appears
Electricity bills, battery capacities and grid statistics.
Joule or kilowatt-hour?
A joule is worth 2.78 × 10⁻⁷ kWh, so the kWh number is 3.6 million times smaller. 1 GJ equals 278 kWh, and 3.6 × 10¹² J equals 1 GWh. The energy is identical; the number and the unit change.
The conversion is exact. The usual trap is direction: from joules to kWh the figure falls steeply.
Where the conversion shows up
Coin cells and wearables
A CR2032 coin cell of 225 mAh at 3 V stores 0.675 Wh, 2,430 J, which is 0.000675 kWh. A smartwatch battery of 1.1 Wh holds 3,960 J, a wireless earbud of 0.2 Wh 720 J. A thousand coin cells hold less than one kilowatt-hour.
Medical implants
A pacemaker pulse needs about 25 µJ, and at 70 beats a minute that is roughly 2.5 J a day, 7 × 10⁻⁷ kWh. The battery of 1 Ah at 2.8 V holds 10,080 J, 0.0028 kWh, enough for around ten years once electronics are included.
Flashes and shocks
A xenon camera flash stores 50 J, 1.39 × 10⁻⁵ kWh. A defibrillator charges to 200 J, 5.6 × 10⁻⁵ kWh. Delivering a tiny energy in a few milliseconds is what makes them powerful.
Wireless sensors
A low-power sensor that transmits a short message uses about 100 mJ per transmission, which is 2.8 × 10⁻⁸ kWh. Sending one message an hour, 24 a day, takes 2.4 J, 6.7 × 10⁻⁷ kWh. A coin cell of 2,430 J would last a thousand days on the radio alone, before sleep current is counted.
Brain and nerves
A single neural impulse costs about 10⁻⁹ J. The brain uses roughly 20 W, 72,000 J an hour, 0.02 kWh, mostly for maintaining the electrical state of its cells. Those figures put a human brain below the consumption of a light bulb, and a “convert J to kWh” calculation makes the comparison exact.
The energy of a keystroke
Pressing a key takes about 0.05 J of mechanical work, 1.4 × 10⁻⁸ kWh. Typing 10,000 characters a day uses 500 J, 0.00014 kWh. Typing all day is cheaper than a single minute of a kettle, which uses 120,000 J, as a “convert J to kWh” calculation confirms.
Mechanical watches
A fully wound mainspring holds about 1 J. A mechanical movement needs roughly 7 µW to run, so that single joule lasts about 40 hours. In kilowatt-hours it is 2.8 × 10⁻⁷ kWh. A wrist-worn watch gains a few joules a day from the motion of the arm through the winding rotor.
Capacitors and supercapacitors
A capacitor of 1 F at 5 V stores 12.5 J, 3.5 × 10⁻⁶ kWh. A supercapacitor module of 3,000 F at 2.7 V stores 10.9 kJ, 0.003 kWh. Banks of them can start diesel engines or buffer wind turbines, with energies of tens of kilojoules.
Cameras and displays
A camera shot at a flash of 50 J, 1.4 × 10⁻⁵ kWh, uses far less than the screen that follows. A 5 W screen showing the picture for one minute spends 300 J, 8.3 × 10⁻⁵ kWh. The flash is spectacular, but the display costs more over time.
Mental conversion
To convert J to kWh in your head, divide by 3.6 and shift six places. 7.2 MJ gives 2 kWh, 36 MJ gives 10 kWh and 3.6 GJ gives 1,000 kWh. If the energy is in kJ, divide by 3.6 and shift three places.
Spreadsheet formulas
To convert J to kWh in a spreadsheet, put the energies in joules in column A and type =A2/3600000 in column B. For the reverse, =B2*3600000. For tiny values, format column B in scientific notation, or compute watt-hours with =A2/3600.
Digits to keep
Datasheet energies are typically good to 10 per cent, so two significant figures are right. A “convert J to kWh” calculation for a coin cell turns 2,430 J into 0.00068 kWh, not 0.000675, since more digits would imply an accuracy the specification lacks.
Landmarks to memorise
1 MJ is 0.278 kWh. 3.6 MJ is 1 kWh. 1 GJ is 278 kWh. 3.6 GJ is 1 MWh. 1 TJ is 278 MWh. 3.6 TJ is 1 GWh. 1 PJ is 278 GWh. Use them to convert J to kWh by eye.
Reference ladder
1,000 J is 0.000278 kWh. 100,000 J is 0.0278 kWh. 10 MJ is 2.78 kWh. 500 MJ is 139 kWh. 10 GJ is 2,778 kWh. 1 TJ is 277,778 kWh. 1 PJ is 277.8 million kWh. A ladder like this makes checks quick.
The sleep current budget
A sensor sleeping at 2 µA on 3 V draws 6 µW, 0.52 J a day, 1.4 × 10⁻⁷ kWh. In a year that is 190 J, 5.3 × 10⁻⁵ kWh. Designers fight for every microamp, because with a battery of 2,430 J even tiny currents matter over years.
Checking by reversing
To check a “convert J to kWh” calculation result, multiply the answer by 3,600,000. If 7,200,000 J became 2 kWh, then 2 times 3,600,000 returns 7,200,000. A second test is size: the kWh figure has six fewer digits.
Link to watt-hours
One Wh is 3,600 J, and one kWh is 1,000 Wh. A coin cell of 2,430 J is 0.675 Wh. A phone battery of 54,000 J is 15 Wh. Battery makers quote Wh, power companies kWh, and physicists J.
A worked example
A farm installs 2,000 soil sensors that each use 60 J a day. The fleet uses 120 kJ a day, 0.033 kWh. In a year that is 43.8 MJ, 12 kWh, which costs a few euros. The batteries, not the electricity, are the expense.
A billion devices
A billion sensors each using 50 J a day need 5 × 10¹⁰ J a day, 13,900 kWh. In a year that is 5 GWh, 18 TJ. A medium power plant of 500 MW makes about 4,400 GWh a year, so even a billion low-power devices need about a thousandth of its output. A “convert J to kWh” calculation puts such a project in perspective.
Power and energy again
A power of 1 mW lasting a day is 86.4 J, 2.4 × 10⁻⁵ kWh. One watt lasting a year is 31.5 MJ, 8.76 kWh. The joule is the energy of one watt over one second, so every energy is a power multiplied by a time.
X-rays and radiotherapy
A chest X-ray deposits an absorbed dose of around 0.1 mGy, which in a 70 kg body is roughly 7 mJ, 2 × 10⁻⁹ kWh. A radiotherapy fraction of 2 Gy delivers 2 J per kilogram to the treated tissue, 140 J if the whole body received it, 3.9 × 10⁻⁵ kWh. Radiation doses are small in energy but large in effect.
Muscle work
Climbing a flight of stairs of 3 metres with 70 kg takes 2,060 J of work, 5.7 × 10⁻⁴ kWh. A hundred flights cost 206 kJ, 0.057 kWh. The body spends about four times as much because of its efficiency.
An alternative path
Joules reach kWh directly by division by 3,600,000, or through watt-hours: divide by 3,600, then by 1,000. When the two paths disagree, a digit has been mistyped.
Hearing aids and earbuds
A hearing-aid battery of size 312 holds about 180 mAh at 1.4 V, which is 0.25 Wh, 900 J. At a drain of 1 mW it runs for 10 days. In kilowatt-hours it is 0.00025 kWh. A box of 100 such cells carries 0.025 kWh, less than a single boiled kettle.
Digital cameras and drones
A compact camera battery of 7 Wh holds 25,200 J, 0.007 kWh, enough for 300 shots. That works out at 84 J for each photograph. A small drone battery of 40 Wh holds 144 kJ, 0.04 kWh, and flies for around 30 minutes, since the rotors draw about 80 W.
Energy harvesting
A vibration harvester producing 100 µW yields 8.6 J a day, 2.4 × 10⁻⁶ kWh. A footstep on a piezoelectric tile gives a few joules, about 2 to 5 J, 5.6 × 10⁻⁷ to 1.4 × 10⁻⁶ kWh. A thousand steps a day gives 5 kJ, 0.0014 kWh. These sources can run sensors but not lamps.
Hearing the numbers: a doorbell
A wireless doorbell transmitter uses a 12 V battery of 55 mAh, 2,376 J, and each press spends about 0.5 J, so the battery lasts for nearly 5,000 presses. In kilowatt-hours that is 0.00066 kWh of stored energy and 1.4 × 10⁻⁷ kWh for every ring. A family that rings 20 times a day wears out the battery in 8 months.
Solar cells in small devices
A calculator cell of 5 cm² in indoor light produces about 100 µW, which is 8.6 J a day. A pocket panel of 10 cm² in sunlight gives 0.1 W, 360 J an hour, 0.0001 kWh. A thousand such panels in full sun would generate 0.1 kWh an hour.
Lighting a lamp
An LED of 1 W burning for an hour uses 3,600 J, 0.001 kWh. A 10 W lamp for 10 hours takes 360,000 J, 0.1 kWh. A string of fairy lights of 5 W on for 6 hours uses 108,000 J, 0.03 kWh. Cheap bulbs therefore cost very little to run.
Charging a phone
A phone battery of 15 Wh holds 54,000 J, 0.015 kWh. A full charge a day for a year takes 5.5 kWh, 19.7 MJ. Even a billion phones charging daily use 5.5 TWh a year, roughly one tenth of a medium-sized country's electricity.
Laptops and tablets
A laptop battery of 60 Wh stores 216 kJ, 0.06 kWh, and a tablet of 30 Wh 108 kJ. Charging a laptop each day costs 22 kWh a year, 79 MJ. A “convert J to kWh” calculation for a battery rating places it beside the energy of household appliances.
The muscle and the spark
A piezo igniter in a gas lighter generates a spark of about 10 mJ, 2.8 × 10⁻¹⁰ kWh. A static discharge from a person can reach 5 mJ. These are tiny energies but large voltages, enough to ignite a gas mixture.
A heartbeat
The human heart does about 1 J of mechanical work per beat. At 70 beats a minute that is 100,800 J a day, 0.028 kWh, and about 37 MJ a year. The body spends many times more as heat, since the heart is only 20 to 25 per cent efficient. The heart's work is still tiny next to a household's yearly use.
More values for convert J to kWh
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 J = 0.0000000277778 kWh
- 0.5 J = 0.000000138889 kWh
- 3 J = 0.000000833333 kWh
- 4 J = 0.00000111111 kWh
- 7 J = 0.00000194444 kWh
- 15 J = 0.00000416667 kWh
- 20 J = 0.00000555556 kWh
- 75 J = 0.0000208333 kWh
- 200 J = 0.0000555556 kWh
- 500 J = 0.000138889 kWh
- 2,000 J = 0.000555556 kWh
- 10,000 J = 0.00277778 kWh
Common slips with a “convert J to kWh” calculation
Multiplying by 3,600,000
From joules to kWh the number falls. If 7,200,000 J became 2.6 × 10¹³, you multiplied instead of dividing.
Confusing W and Wh
The watt is power and the watt-hour energy. A 5 W device does not use 5 Wh unless it runs for an hour. Read the unit carefully before converting.
mJ and µJ
A millijoule is a thousandth of a joule and a microjoule a millionth. Mixing them gives a factor of a thousand. In low-power electronics the prefix is the whole story.
Questions in brief
What is the formula to convert J to kWh?
kWh equals joules divided by 3,600,000.
What is a million joules in kWh?
0.278 kWh.
What is a billion joules in kWh?
278 kWh.
What is 1 kWh in joules?
Exactly 3,600,000 J.
Is my input uploaded?
No, it is all computed in your browser.
Related pages and a summary
You may also want Convert J to cal, Convert cal to kWh, Convert BTU to kWh, Convert kWh to cal, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert ft/s to mph. For the opposite direction, see Convert kWh to J.
Summing up: joules become kilowatt-hours when divided by 3,600,000, and the unit goes beside the answer. Everything stays in your browser, with no account and no upload.