Energy Converter
Convert energy between scientific, food and electrical units: joules for physics, kilocalories and kilojoules for nutrition, and kilowatt-hours for electricity and batteries.
kilojoules
1 kcal = 4.184 kJ
Popular energy conversions
Units in this converter
| Unit | Symbol | Equals (in joules) |
|---|---|---|
| Joule | J | 1 J |
| Kilojoule | kJ | 1,000 J |
| Calorie (small, thermochemical) | cal | 4.184 J |
| Kilocalorie (food Calorie) | kcal | 4,184 J |
| Watt-hour | Wh | 3,600 J |
| Kilowatt-hour | kWh | 3,600,000 J |
Calories on food labels
The “calories” on food packaging are kilocalories (kcal). A 250 kcal snack contains 250,000 small calories. This converter lists the small calorie and the kilocalorie separately so you can pick the right one.
The calorie used is the thermochemical calorie, exactly 4.184 J. Other historical definitions differ by less than 0.1%.
About the units
- Joule (J)
- The joule is the SI unit of energy. One joule is the work done by a force of one newton over one meter, or one watt of power for one second.
- Kilojoule (kJ)
- A kilojoule is 1,000 joules. Food labels in the EU, Australia and New Zealand show energy in kilojoules, usually next to kilocalories.
- Calorie (small, thermochemical) (cal)
- The calorie used here is the thermochemical calorie, exactly 4.184 joules: roughly the energy needed to warm one gram of water by 1 °C. Food labels that say "calories" actually mean kilocalories.
- Kilocalorie (food Calorie) (kcal)
- A kilocalorie is 1,000 calories, or 4,184 joules. It is the "Calorie" on food labels, sometimes written with a capital C.
- Watt-hour (Wh)
- A watt-hour is the energy of one watt sustained for one hour, which is 3,600 joules. Battery capacities, such as power banks and laptop batteries, are often given in watt-hours.
- Kilowatt-hour (kWh)
- A kilowatt-hour is 1,000 watt-hours, or 3.6 million joules. Electricity bills and electric car batteries are measured in kilowatt-hours.
Frequently asked questions
Are food calories the same as kilocalories?
Yes. A food Calorie (sometimes with a capital C) is one kilocalorie, which is 4.184 kilojoules.
How many joules are in a kilowatt-hour?
Exactly 3,600,000 joules (3.6 megajoules): 1,000 watts × 3,600 seconds.