How to convert energy
The joule is the SI unit of energy: one watt of power for one second. A kilowatt-hour, the “unit” on your electricity bill, is 1,000 W for an hour, which is 3.6 million joules. Food energy uses the kilocalorie (written “Calorie” on labels): 1 kcal = 4.184 kJ.
- kcal to kJ: multiply by 4.184 (2,000 kcal = 8,368 kJ).
- kWh to BTU: multiply by 3,412.14.
- Electricity units to MJ: 1 kWh = 3.6 MJ.
The calorie here is the thermochemical calorie (4.184 J), which is the one used for food labels. The International Table calorie is slightly larger (4.1868 J). The BTU is the International Table BTU.
Common energy conversion factors
| Unit | Equals | Reverse |
|---|---|---|
| 1 kilowatt-hour (unit) | 36,00,000 J | 1 joule = 2.7777778 × 10⁻⁷ kWh |
| 1 kilocalorie (food Calorie) | 4.184 kJ | 1 kilojoule = 0.2390057361 kcal |
| 1 calorie | 4.184 J | 1 joule = 0.2390057361 cal |
| 1 British thermal unit | 1.055055853 kJ | 1 kilojoule = 0.9478171203 BTU |
| 1 kilowatt-hour (unit) | 3,412.141633 BTU | 1 British thermal unit = 0.0002930711 kWh |
| 1 joule | 6.2415091 × 10¹⁸ eV | 1 electronvolt = 1.6021766 × 10⁻¹⁹ J |
| 1 watt-hour | 3,600 J | 1 joule = 0.0002777778 Wh |
| 1 therm (US) | 29.30011111 kWh | 1 kilowatt-hour (unit) = 0.0341295634 thm |
| 1 kilocalorie (food Calorie) | 0.0011622222 kWh | 1 kilowatt-hour (unit) = 860.4206501 kcal |
| 1 foot-pound | 1.355817948 J | 1 joule = 0.7375621493 ft·lbf |
| 1 megajoule | 0.2777777778 kWh | 1 kilowatt-hour (unit) = 3.6 MJ |
Energy conversions
Each of these has its own page with the formula, worked examples and a full conversion table:
All energy units on this converter
| Unit | Symbol | 1 unit equals | System |
|---|---|---|---|
| Joule | J | 1 J | Metric (SI) |
| Kilojoule | kJ | 1,000 J | Metric (SI) |
| Megajoule | MJ | 10,00,000 J | Metric (SI) |
| Gigajoule | GJ | 1,00,00,00,000 J | Metric (SI) |
| Watt-hour | Wh | 3,600 J | Electrical |
| Kilowatt-hour (unit) | kWh | 36,00,000 J | Electrical |
| Megawatt-hour | MWh | 3,60,00,00,000 J | Electrical |
| Calorie | cal | 4.184 J | Heat & food |
| Kilocalorie (food Calorie) | kcal | 4,184 J | Heat & food |
| British thermal unit | BTU | 1,055.055853 J | Heat & food |
| Therm (US) | thm | 10,54,80,400 J | Heat & food |
| Electronvolt | eV | 1.6021766 × 10⁻¹⁹ J | Science |
| Erg | erg | 1 × 10⁻⁷ J | Science |
| Foot-pound | ft·lbf | 1.355817948 J | Science |
| Tonne of oil equivalent | toe | 41,86,80,00,000 J | Science |
Frequently asked questions
How many joules are in a kWh?
1 kilowatt-hour = 3,600,000 joules (3.6 MJ).
Is a food Calorie the same as a calorie?
No. A food Calorie (capital C) is a kilocalorie, 1,000 calories or 4.184 kJ. Food labels in India and many countries show kcal and kJ.
What is an electricity unit?
One unit on an Indian electricity bill is 1 kilowatt-hour: a 1,000 W appliance running for one hour.
How many BTU is 1 kWh?
1 kWh = 3,412.14 BTU. 1 BTU = 0.000293 kWh (0.293 Wh).