Energy converter

Convert energy between joules, calories, kilowatt-hours and BTU. 1 kcal (a food Calorie) is 4.184 kJ, and 1 kWh is 3.6 MJ.

Value

From

Result

1 kcal = 4.184 kJ

Digits

Same amount, two scales

100 kcal

418.4 kJ

Both bars show the same amount: 100 kcal on top, 418.4 kJ below.

Quick challenge

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Guess the conversion before you calculate it. How many can you get in a row?

How it works

Energy is converted through the joule. Nutrition labels show kilocalories (often written “Calories”) or kilojoules; electricity bills use kWh; heating and air conditioning use BTU. This converter uses the thermochemical calorie (4.184 J).

All units compared

All units compared
Unit	Symbol	Value in joules
joule	J	1 J
kilojoule	kJ	1,000 J
megajoule	MJ	1,000,000 J
calorie	cal	4.184 J
kilocalorie	kcal	4,184 J
watt-hour	Wh	3,600 J
kilowatt-hour	kWh	3,600,000 J
British thermal unit	BTU	1,055.055853 J
foot-pound	ft·lbf	1.355817948 J
electronvolt	eV	1.602176634E-19 J

Frequently asked questions

Are calories on food labels kilocalories?

Yes. A food “Calorie” is a kilocalorie (1,000 small calories), equal to 4.184 kJ.

How many BTU are in a kWh?

About 3,412 BTU. 1 BTU is about 1,055 joules.

How many kilojoules are in 1 kilocalorie?

1 kilocalorie = 4.184 kilojoules. The other way round, 1 kilojoule = 0.239006 kilocalories.

How many kilocalories are in 1 kilojoule?

1 kilojoule = 0.239006 kilocalories. The other way round, 1 kilocalorie = 4.184 kilojoules.