Energy Converter
Convert values between joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour and BTU in real time, right in your browser.
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How it works
Joule and kilojoule are units of the International System. Calorie and kilocalorie are common in nutrition (the "Calorie" on food labels is actually a kilocalorie). Watt-hour and kilowatt-hour show up on electricity bills, and the BTU is used mainly to rate air conditioners. One kilocalorie equals 4.184 kilojoules. On an electricity bill, energy comes in kilowatt-hours: a 1,000 W appliance running for an hour uses 1 kWh, or 3.6 million joules. A 10 W bulb left on for 100 hours uses the same 1 kWh. On food labels, the "Calorie" is the kilocalorie: a 2,000 kcal diet is 8,368 kJ. And the air conditioner BTU deserves a caveat: capacity is given in BTU per hour, which is power; this converter handles energy only, so 12,000 BTU is about 12.66 million joules (roughly 3.5 kWh).