Energy converter
Convert between any two of 9 energy units. Conversion runs in your browser.
More detailsUnits covered · Everyday energy conversions · Which calorie · Energy and power are different quantities
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 |
Everyday energy conversions
| 1 of these | J | kJ | cal | kcal | kWh |
|---|---|---|---|---|---|
| Joule | 1 | 0.001 | 0.2390057 | 0.0002390057 | 2.777778e-07 |
| Kilojoule | 1,000 | 1 | 239.005736 | 0.2390057 | 0.0002777778 |
| Calorie | 4.184 | 0.004184 | 1 | 0.001 | 0.000001162222 |
| Kilocalorie | 4,184 | 4.184 | 1,000 | 1 | 0.001162222 |
| Kilowatt hour | 3,600,000 | 3,600 | 860,420.7 | 860.42065 | 1 |
Each row is one of that unit, given in each of the others.
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.