Energy converters
20 conversions between 9 energy units. Every page includes a live converter, the formula and a full conversion table.
Units covered
| Unit | Symbol | In joules |
|---|---|---|
| Joule | J | 1 |
| Kilojoule | kJ | 1,000 |
| Calorie | cal | 4.184 |
| Kilocalorie | kcal | 4,184 |
| Watt hour | Wh | 3,600 |
| Kilowatt hour | kWh | 3,600,000 |
| British thermal unit | BTU | 1,055.056 |
| Electronvolt | eV | 1.602177e-19 |
| Foot pound | ft⋅lb | 1.355818 |
All energy conversions
- Joules to Kilojoules
- Joules to Calories
- Joules to Kilocalories
- Joules to Kilowatt Hours
- Kilojoules to Joules
- Kilojoules to Calories
- Kilojoules to Kilocalories
- Kilojoules to Kilowatt Hours
- Calories to Joules
- Calories to Kilojoules
- Calories to Kilocalories
- Calories to Kilowatt Hours
- Kilocalories to Joules
- Kilocalories to Kilojoules
- Kilocalories to Calories
- Kilocalories to Kilowatt Hours
- Kilowatt Hours to Joules
- Kilowatt Hours to Kilojoules
- Kilowatt Hours to Calories
- Kilowatt Hours to Kilocalories
Which calorie
The word covers two units differing by a factor of a thousand. The small calorie is the energy to heat one gram of water by one degree Celsius, about 4.184 J. The large calorie, or kilocalorie, is a thousand of those. Food labelling uses the large one but almost always writes it with a small c, so a 200-calorie snack is really 200 kcal, or about 837 kJ. Labels outside the US usually give both.
Energy and power are different quantities
A watt is a rate; a joule is an amount. Multiplying a rate by a time gives an amount, which is where the kilowatt-hour comes from: a kilowatt sustained for an hour, or 3.6 million joules. Electricity is billed in kilowatt-hours because the meaningful question is how much energy was delivered, not how fast. If a figure is quoted in watts, it belongs in power rather than here.