Convert Joules to Kilojoules
1 joule is 0.001 kJ. One joule is exactly 0.001 kilojoules.
One joule is 0.001 kilojoules. To convert joules to kilojoules, multiply by 0.001; to go the other way, divide by 0.001 or multiply by 1000. The factor is exact rather than rounded: it follows from NIST Special Publication 811. The SI unit: one newton acting through one metre.
Factor checked against the defining standard · How we check
- Joules × 0.001
value * 0.0010.001 kJ
1 joule in every energy unit
| Unit | Value | Exact factor |
|---|---|---|
| joules (as entered) | 1 J | — |
| kilojoules | 0.001 kJ | × 0.001 |
| calories | 0.2390057361 cal | × 0.239005736138 |
| kilocalories | 0.0002390057361 kcal | × 0.000239005736138 |
| watt-hours | 0.0002777777778 Wh | × 0.000277777777778 |
| kilowatt-hours | 0.0000002777777778 kWh | × 0.000000277777777778 |
| British thermal units | 0.0009478171203 BTU | × 0.000947817120313 |
| foot-pounds | 0.7375621493 ft·lbf | × 0.737562149277 |
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 joules to kilojoules?
- 1.Take the measurement in joules.
- 2.Multiply by 0.001 — that is how many kilojoules fit in one joule.
- 3.To go back the other way, divide by 0.001, or multiply by 1000.
Worked example: 25 joules to kilojoules
- Formula
- J × 0.001 = kJ
- Arithmetic
- 25 × 0.001 = 0.025 kJ
- Answer
- 25 J = 0.025 kJ
The factor is exact, so this figure is exact too — only the display is rounded.
Joules to kilojoules conversion table
| Joules | Kilojoules |
|---|---|
| 1 J | 0.001 kJ |
| 2 J | 0.002 kJ |
| 3 J | 0.003 kJ |
| 4 J | 0.004 kJ |
| 5 J | 0.005 kJ |
| 6 J | 0.006 kJ |
| 7 J | 0.007 kJ |
| 8 J | 0.008 kJ |
| 9 J | 0.009 kJ |
| 10 J | 0.01 kJ |
| 12 J | 0.012 kJ |
| 15 J | 0.015 kJ |
| 20 J | 0.02 kJ |
| 25 J | 0.025 kJ |
| 50 J | 0.05 kJ |
| 100 J | 0.1 kJ |
| 200 J | 0.2 kJ |
| 300 J | 0.3 kJ |
| 500 J | 0.5 kJ |
| 1000 J | 1 kJ |
| 2000 J | 2 kJ |
| 5000 J | 5 kJ |
| 10000 J | 10 kJ |
What is a joule?
The SI unit: one newton acting through one metre. Dropping a small apple one metre releases about one joule.
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 joule?
One joule is 0.001 kilojoules, exactly. Going the other way, one kilojoule is 1000 joules. 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 joule?
- 0.001. A thousand joules. Food energy outside the US is labelled here, alongside or instead of calories.
- How do I convert kilojoules back to joules?
- Divide by 0.001, or multiply by 1000 — they are the same operation.
Other energy conversions
Kilojoules to joules — the same conversion the other way.