Convert Watt-hours to Kilojoules
1 watt-hour is 3.6 kJ. One watt-hour is exactly 3.6 kilojoules.
One watt-hour is 3.6 kilojoules. To convert watt-hours to kilojoules, multiply by 3.6; to go the other way, divide by 3.6 or multiply by 0.27777778. The factor is exact rather than rounded: it follows from NIST Special Publication 811. One watt sustained for an hour, so exactly 3,600 joules.
Factor checked against the defining standard · How we check
- Watt-hours × 3.6
value * 3.63.6 kJ
1 watt-hour in every energy unit
| Unit | Value | Exact factor |
|---|---|---|
| joules | 3,600 J | × 3,600 |
| kilojoules | 3.6 kJ | × 3.6 |
| calories | 860.4206501 cal | × 860.420650096 |
| kilocalories | 0.8604206501 kcal | × 0.860420650096 |
| watt-hours (as entered) | 1 Wh | — |
| kilowatt-hours | 0.001 kWh | × 0.001 |
| British thermal units | 3.412141633 BTU | × 3.41214163313 |
| foot-pounds | 2,655.223737 ft·lbf | × 2,655.2237374 |
Factors are entered by hand from NIST Special Publication 811 rather than derived from a units library, so the ones that terminate are exact rather than rounded.
How do you convert watt-hours to kilojoules?
- 1.Take the measurement in watt-hours.
- 2.Multiply by 3.6 — that is how many kilojoules fit in one watt-hour.
- 3.To go back the other way, divide by 3.6, or multiply by 0.27777778.
Worked example: 25 watt-hours to kilojoules
- Formula
- Wh × 3.6 = kJ
- Arithmetic
- 25 × 3.6 = 90 kJ
- Answer
- 25 Wh = 90 kJ
The factor is exact, so this figure is exact too — only the display is rounded.
Watt-hours to kilojoules conversion table
| Watt-hours | Kilojoules |
|---|---|
| 1 Wh | 3.6 kJ |
| 2 Wh | 7.2 kJ |
| 3 Wh | 10.8 kJ |
| 4 Wh | 14.4 kJ |
| 5 Wh | 18 kJ |
| 6 Wh | 21.6 kJ |
| 7 Wh | 25.2 kJ |
| 8 Wh | 28.8 kJ |
| 9 Wh | 32.4 kJ |
| 10 Wh | 36 kJ |
| 12 Wh | 43.2 kJ |
| 15 Wh | 54 kJ |
| 20 Wh | 72 kJ |
| 25 Wh | 90 kJ |
| 50 Wh | 180 kJ |
| 100 Wh | 360 kJ |
| 200 Wh | 720 kJ |
| 300 Wh | 1,080 kJ |
| 500 Wh | 1,800 kJ |
| 1000 Wh | 3,600 kJ |
| 2000 Wh | 7,200 kJ |
| 5000 Wh | 18,000 kJ |
| 10000 Wh | 36,000 kJ |
What is a watt-hour?
One watt sustained for an hour, so exactly 3,600 joules. Battery capacity is quoted here because it is an amount of energy rather than a rate.
What is a kilojoule?
A thousand joules. Food energy outside the US is labelled here, alongside or instead of calories.
How many kilojoules are in a watt-hour?
One watt-hour is 3.6 kilojoules, exactly. Going the other way, one kilojoule is 0.27777778 watt-hours. Both figures come from the same defined relation rather than from a measurement, which is why they are the same today as they were in 1959.
Every energy unit here
| Unit | Symbol | One of these is |
|---|---|---|
| Joules | J | the base unit |
| Kilojoules | kJ | 1000 joule |
| Calories | cal | 4.184 joule |
| Kilocalories | kcal | 4184 joule |
| Watt-hours | Wh | 3600 joule |
| Kilowatt-hours | kWh | 3600000 joule |
| British thermal units | BTU | 1055.0559 joule |
| Foot-pounds | ft·lbf | 1.3558179 joule |
Source: NIST Special Publication 811 — the thermochemical calorie is exactly 4.184 J
Questions people actually ask
- How many kilojoules are in a watt-hour?
- 3.6. A thousand joules. Food energy outside the US is labelled here, alongside or instead of calories.
- How do I convert kilojoules back to watt-hours?
- Divide by 3.6, or multiply by 0.27777778 — they are the same operation.
Other energy conversions
Kilojoules to watt-hours — the same conversion the other way.