Energy is measured in units such as J, kJ, Wh, kWh, cal, kcal, BTU. Pick a source and target unit above, enter a value, and the result appears instantly — free and entirely in your browser. Below you'll find the most common individual conversions as dedicated pages.
Which energy units are there?
- Joule (J) — The joule (J) is the SI unit of energy: the work done by one newton acting over one metre. It is small for everyday use, so kilojoules, kilocalories and kilowatt-hours are more common.
- Kilojoule (kJ) — The kilojoule (kJ) equals 1,000 joules. It is the SI energy unit on European food labels, usually shown next to kilocalories.
- Watt-hour (Wh) — The watt-hour (Wh) is the energy of one watt sustained for one hour, equal to 3,600 joules. It rates small batteries and power banks.
- Kilowatt-hour (kWh) — The kilowatt-hour (kWh) is 1,000 watt-hours (3.6 MJ) and the unit on your electricity bill. A typical home uses several kWh per day.
- Calorie (cal) — The calorie (cal) is roughly the energy to warm one gram of water by 1 °C, about 4.184 joules. The 'calories' on food labels are actually kilocalories.
- Kilocalorie (kcal) — The kilocalorie (kcal), also written Calorie, equals 1,000 calories or 4.184 kJ. It is the food-energy unit used in nutrition worldwide.
- British thermal unit (BTU) — The British thermal unit (BTU) is roughly the energy to heat one pound of water by 1 °F, about 1,055 joules. It rates heating, boilers and air conditioners, especially in the US.
Key facts about energy
Energy units come from different fields: joules and kilojoules in physics, kilocalories on food labels, kilowatt-hours on electricity bills, BTU in heating and air-conditioning. Converting between them is common for nutrition, utility bills and HVAC.
One kilocalorie (the food Calorie) equals exactly 4.184 kJ — which is why nutrition labels show both. One kilowatt-hour is 3.6 MJ, equal to about 3,412 BTU or 860 kcal (BIPM/ISO).
How to use the energy converter
- Pick the source unit and enter the energy value.
- Pick the target unit — the result appears instantly.
- Use the swap button to reverse the direction.
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