⚡ Energy Converter
Convert between joules, calories, kilowatt-hours and BTU. Food energy, electricity bills and heating capacity each use different units, 1 food Calorie (kcal) = 4,184 joules.
1 J = 0.001 kJ
1 joules = 0.001 kilojoules
1 × 0.001 = 0.001
1 J equals 0.001 kJ, so multiplying by 0.001 converts the value. The result describes the exact same quantity, only the measuring stick changes.
Popular energy conversions
All energy units
| Unit | Symbol | Definition |
|---|---|---|
| Joule | J | The joule (J) is the SI unit of energy, the work done by a one-newton force over one meter. All other energy units are defined in joules. |
| Kilojoule | kJ | A kilojoule (kJ) is 1,000 joules. Food energy on labels in Australia, NZ and the EU is stated in kilojoules alongside or instead of kilocalories. |
| Calorie (small) | cal | A small (gram) calorie (cal) is exactly 4.184 joules, the energy to heat 1 gram of water by 1 °C. Note that food "Calories" are actually kilocalories (1,000 small calories). |
| Kilocalorie | kcal | A kilocalorie (kcal) is 4,184 joules, identical to the food "Calorie" (capital C) on US nutrition labels. A 2,000-Calorie diet is 2,000 kcal or 8,368 kJ. |
| Watt-hour | Wh | A watt-hour (Wh) is 3,600 joules, one watt sustained for an hour. Phone and laptop battery capacities are commonly given in watt-hours. |
| Kilowatt-hour | kWh | A kilowatt-hour (kWh) is 3.6 million joules, the unit on your electricity bill. Running a 1,000 W appliance for one hour uses exactly 1 kWh. |
| British thermal unit | BTU | A British thermal unit (BTU) is about 1,055 joules, the energy to heat one pound of water by 1 °F. Air conditioners and heaters are rated in BTU per hour. |
| Foot-pound | ft⋅lb | A foot-pound (ft⋅lb) is the energy of one pound-force acting over one foot, about 1.3558 joules. Torque wrench settings and muzzle energies use foot-pounds. |
Frequently asked questions
How do I convert energy units?
Choose your two units in the converter above and type a value, the result updates instantly, entirely in your browser. All 8 energy units on this page are interchangeable, so you can convert in either direction.
Which energy units can I convert here?
This converter supports 8 energy units: Joule (J), Kilojoule (kJ), Calorie (small) (cal), Kilocalorie (kcal) and 4 more. Pick any two to convert between them.
What is the most common energy conversion?
One of the most-used energy conversions is Kilocalories to Kilojoules (kcal → kJ). Every energy pair we support is linked below, each with its own formula and table.
Is this Energy Converter free and private?
Yes. It is free with no sign-up, uses the exact internationally defined conversion factors, and computes every result locally in your browser, nothing you type is uploaded, and the page keeps working offline.