Energy converter

Convert joules, calories, kilowatt-hours and more

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How it works

To convert energy, multiply it by the size of the first unit in joules, then divide by the size of the second. One kilocalorie is 4,184 joules, and one kilowatt-hour is exactly 3.6 million joules. Food labels call a kilocalorie a calorie, so check which one you have.

result = value × joules in first unit ÷ joules in second unit

The joule is the SI unit of energy. We use the thermochemical calorie of exactly 4.184 joules. One kilowatt-hour is one kilowatt used for 3,600 seconds.

Worked example. To change 100 kilocalories to kilojoules: 100 × 4.184 = 418.4 kilojoules.

Examples

From	To
1 Kilocalories	≈ 4.18 Kilojoules
1 Kilowatt-hours	3.6 Megajoules
1 Kilowatt-hours	≈ 860.42 Kilocalories
1 British thermal units	≈ 1,055.06 Joules

What this tool doesn’t cover

There are several definitions of the calorie and the BTU. We use the common ones and name them.
Results show up to two decimal places.

Questions

Is a food calorie the same as a calorie?

No. A food Calorie is a kilocalorie, which is 1,000 small calories.

How many joules are in a kilowatt-hour?

One kilowatt-hour is exactly 3,600,000 joules.

What is a kilowatt-hour used for?

It is the unit on electricity bills. In India, it is often called a unit.

How many calories are in a kilojoule?

One kilojoule is about 0.239 food calories, or kcal. One kcal is about 4.184 kJ.

How do I work out the units on my electricity bill?

One unit on a bill is one kilowatt-hour. A 1,000 watt heater running for one hour uses one unit.

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Sources: NIST Office of Weights and Measures (opens in a new tab), BIPM: SI units (opens in a new tab)