Energy Converter
Convert joules, calories, kilowatt hours, BTU and foot-pounds.
All units
About this tool
Convert between joules, kilojoules and megajoules, small calories and food Calories (kcal), watt hours and kilowatt hours, BTU and foot-pounds. Useful for reading nutrition labels against kJ (common outside the US), comparing an appliance's consumption to your electricity bill, or translating heating specs quoted in BTU.
The factors are exact definitions: a calorie is 4.184 J, a kilowatt hour is 3.6 MJ, a BTU is 1,055.056 J. Type a value, pick two units, and read the answer as you type; the all-units table shows every equivalent at once, and the units you used last are remembered. Everything runs locally in your browser.
Frequently asked questions
- Are food Calories the same as calories?
- A food Calorie (capital C, kcal) is 1,000 small calories. Nutrition labels worldwide use kcal; a 500 Calorie meal is 500 kcal, which is about 2,092 kJ.
- How do kilowatt hours relate to joules?
- A kilowatt hour is the energy of 1,000 watts running for an hour: exactly 3.6 megajoules. It is the unit on your electricity bill.
- Is my input sent anywhere?
- No. The conversion runs in your browser with plain JavaScript, so nothing is uploaded and it works offline once the page has loaded.
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