Convert Calories to Kilojoules
1 calorie is 0.004184 kJ. One calorie is exactly 0.004184 kilojoules.
One calorie is 0.004184 kilojoules. To convert calories to kilojoules, multiply by 0.004184; to go the other way, divide by 0.004184 or multiply by 239.00574. The factor is exact rather than rounded: it follows from NIST Special Publication 811. The thermochemical calorie: exactly 4.184 joules by definition.
Factor checked against the defining standard · How we check
- Calories × 0.004184
value * 0.0041840.004 kJ
1 calorie in every energy unit
| Unit | Value | Exact factor |
|---|---|---|
| joules | 4.184 J | × 4.184 |
| kilojoules | 0.004184 kJ | × 0.004184 |
| calories (as entered) | 1 cal | — |
| kilocalories | 0.001 kcal | × 0.001 |
| watt-hours | 0.001162222222 Wh | × 0.00116222222222 |
| kilowatt-hours | 0.000001162222222 kWh | × 0.00000116222222222 |
| British thermal units | 0.003965666831 BTU | × 0.00396566683139 |
| foot-pounds | 3.085960033 ft·lbf | × 3.08596003258 |
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 calories to kilojoules?
- 1.Take the measurement in calories.
- 2.Multiply by 0.004184 — that is how many kilojoules fit in one calorie.
- 3.To go back the other way, divide by 0.004184, or multiply by 239.00574.
Worked example: 25 calories to kilojoules
- Formula
- cal × 0.004184 = kJ
- Arithmetic
- 25 × 0.004184 = 0.1046 kJ
- Answer
- 25 cal = 0.1046 kJ
The factor is exact, so this figure is exact too — only the display is rounded.
Calories to kilojoules conversion table
| Calories | Kilojoules |
|---|---|
| 1 cal | 0.004184 kJ |
| 2 cal | 0.008368 kJ |
| 3 cal | 0.012552 kJ |
| 4 cal | 0.016736 kJ |
| 5 cal | 0.02092 kJ |
| 6 cal | 0.025104 kJ |
| 7 cal | 0.029288 kJ |
| 8 cal | 0.033472 kJ |
| 9 cal | 0.037656 kJ |
| 10 cal | 0.04184 kJ |
| 12 cal | 0.050208 kJ |
| 15 cal | 0.06276 kJ |
| 20 cal | 0.08368 kJ |
| 25 cal | 0.1046 kJ |
| 50 cal | 0.2092 kJ |
| 100 cal | 0.4184 kJ |
| 200 cal | 0.8368 kJ |
| 300 cal | 1.2552 kJ |
| 500 cal | 2.092 kJ |
| 1000 cal | 4.184 kJ |
| 2000 cal | 8.368 kJ |
| 5000 cal | 20.92 kJ |
| 10000 cal | 41.84 kJ |
What is a calorie?
The thermochemical calorie: exactly 4.184 joules by definition. This is the small calorie — the one on a food label is a thousand of these, which is the single most common confusion in this group.
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 calorie?
One calorie is 0.004184 kilojoules, exactly. Going the other way, one kilojoule is 239.00574 calories. 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 calorie?
- 0.004184. A thousand joules. Food energy outside the US is labelled here, alongside or instead of calories.
- How do I convert kilojoules back to calories?
- Divide by 0.004184, or multiply by 239.00574 — they are the same operation.
Other energy conversions
Kilojoules to calories — the same conversion the other way.