Energy Converter
Convert between joules, calories, kilocalories and kilowatt-hours, with the formula shown for each conversion.
How energy conversion works
Every unit here is defined against the joule, the SI unit of energy. Converting means dividing by the source unit's factor and multiplying by the target unit's factor, the same base-unit method used by every converter on this site.
1 calorie is exactly 4.184 joules, and 1 kilowatt-hour is exactly 3,600,000 joules (1,000 watts running for 3,600 seconds).
Why a food "Calorie" is actually a kilocalorie
Nutrition labels write "Calories" with a capital C, but they mean kilocalories: 1 food Calorie = 1,000 scientific calories = 1 kcal. A 200-Calorie snack contains 200,000 calories in the small, scientific sense, which sounds alarming until you remember that a scientific calorie is a tiny unit, defined as the energy to heat 1 gram of water by 1°C. This site's kilocalorie unit is what food labels mean by "Calories," so select kcal, not cal, when converting a nutrition label.
Reference points
| Unit | Equal to | Typical use |
|---|---|---|
| 1 kcal | 4,184 J | Nutrition labels ("Calories") |
| 1 kWh | 3,600,000 J | Electricity bills |
| 1 BTU | 1,055.06 J | Air conditioner and heater ratings (US) |
| 1 kWh | 860.42 kcal | Comparing electricity use to food energy |