Energy Converter

Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kWh and BTU.

Kilojoules
8,368 kJ
The same energy in units of similar size
kJkJ — Value: 8,3688,368BTUBTU — Value: 7,931.37,931.334WhWh — Value: 2,324.42,324.444kcalkcal — Value: 2,0002,000
Joules
8,368,000 J
Calories (small)
2,000,000 cal
Kilocalories (food Calories)
2,000 kcal
Watt-hours
2,324.444444 Wh
Kilowatt-hours
2.32444444 kWh
British thermal units
7,931.333663 BTU

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Formula

1 cal (thermochemical) = 4.184 J1 kcal = 1 food Calorie = 4.184 kJ1 Wh = 3,600 J; 1 kWh = 3.6 MJ1 BTU (IT) ≈ 1,055.06 J

How it works

The joule is the SI unit of energy: the work done by a force of one newton over one meter, or one watt of power for one second. Everything else here is a fixed multiple of it.

Food labels say “Calories” but mean kilocalories: a 2,000 Calorie diet is 2,000 kcal, or about 8,370 kJ — the figure printed on labels in Australia and Europe. A small calorie (cal) is the energy to warm one gram of water by about one degree Celsius.

Electricity is billed in kilowatt-hours, and heating and air-conditioning equipment in the US is rated in BTU. One kWh is about 3,412 BTU, which is why a 1.5 kW space heater is roughly a 5,000 BTU/h heater.

Frequently asked questions

How many kJ are in a calorie?

One food Calorie (kcal) is 4.184 kJ. One small calorie is 4.184 J.

How much energy is 1 kWh?

3.6 million joules — enough to run a 100 W bulb for 10 hours, or about 860 food Calories.

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