Energy Converter
Convert between joules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, foot-pounds and electronvolts.
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1 kWh
3,600,000 J
Joule
In every unit
| Unit | Symbol | Value |
|---|---|---|
| Joule | J | 3,600,000 |
| Kilojoule | kJ | 3,600 |
| Calorie | cal | 860,420.7 |
| Kilocalorie | kcal | 860.4207 |
| Watt hour | Wh | 1,000 |
| Kilowatt hour | kWh | 1 |
| British thermal unit | BTU | 3,412.142 |
| Foot-pound | ft·lb | 2,655,224 |
| Electronvolt | eV | 2.246943E+25 |
Electricity bills are in kilowatt-hours, food labels are in kilocalories, heating equipment is often in BTU, and physics is in joules. They all measure the same quantity.
How it works
Every unit is expressed in joules and conversions go through it. A watt is one joule per second, so a watt-hour is 3600 joules and a kilowatt-hour is exactly 3.6 million.
The calorie used here is the thermochemical calorie, defined as exactly 4.184 joules. The BTU is the International Table value, 1055.05585262 joules. Both have other definitions in circulation that differ by less than one per cent; the ones used are named so you can check a result against the right one.
Examples
| Case | Input | Result |
|---|---|---|
| A kilowatt hour off an electricity bill | 1 kWh | 3,600 kJ |
| A food calorie | 1 kcal | 4.184 kJ |
| A British thermal unit | 1 BTU | 1,055.056 J |
Frequently asked questions
Is the calorie on a food label the same calorie?
No, and it is the most common confusion in this family. A food "Calorie" is a kilocalorie — a thousand of the calories in this table. A 200 Calorie snack is 200 kilocalories, about 837 kilojoules, which is why European labels print both.
What does a kilowatt-hour actually measure?
Energy, not power. A kilowatt is a rate; running it for an hour delivers a kilowatt-hour of energy. A 2 kW heater on for thirty minutes uses one kilowatt-hour, and so does a 100 W bulb left on for ten hours.
Why is an electronvolt in the list?
Because it is the natural unit at atomic scale, and seeing how small it is against a joule is the point. It is the energy an electron gains crossing a one volt potential difference: about 1.602 × 10⁻¹⁹ joules.
Good to know
- Every factor used here is an exact definition rather than a rounded measurement, so the only error in a result is the one that comes from displaying it with a finite number of digits.