Convert any energy unit
Pick any two units and convert between them: joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU. The result updates as you type, and negative values are accepted for a change in energy.
Every unit is defined against the joule. The thermochemical calorie is exactly 4.184 J, and a watt-hour is exactly 3,600 J.
Units at a glance
| Unit | Symbol | Size |
|---|---|---|
| joules | J | The base unit for energy. |
| kilojoules | kJ | 1 kilojoule = 1,000 joules |
| calories | cal | 1 calorie = 4.184 joules |
| kilocalories | kcal | 1 kilocalorie = 4,184 joules |
| watt-hours | Wh | 1 watt-hour = 3,600 joules |
| kilowatt-hours | kWh | 1 kilowatt-hour = 3,600,000 joules |
| BTU | BTU | 1 BTU = 1,055.05585262 joules |
Calories and kilocalories
The "Calories" on food labels are kilocalories: 1,000 small calories. A "calorie" with a lower-case c, as in chemistry, is one thousandth of that. This converter keeps them as separate units.
Kilowatt-hours
Electricity is billed in kilowatt-hours, the energy of one kilowatt of power used for one hour. It appears as a "unit" on many UK electricity bills.
Which BTU
There are several slightly different definitions of the British thermal unit. This converter uses the International Table BTU, which is the most common.