Convert energy units

This energy converter switches between the SI unit (joule) and other common units including kilojoules, calories, kilocalories (food calories), watt-hours, kilowatt-hours, and British thermal units (BTU). It is handy for nutrition labels, electricity bills, heating, and physics. Enter a value and the conversion appears instantly.

Food calories explained

The “calories” on food labels are actually kilocalories (kcal) — one food Calorie equals 1,000 small calories, or about 4,184 joules. UK labels usually show both kJ and kcal. So a 250 kcal snack contains roughly 1,046 kJ of energy.

Common energy conversions

From	To	Result
1 kcal	kJ	4.184 kJ
1 kWh	kJ	3,600 kJ
1 BTU	kJ	1.055 kJ

Frequently asked questions

How many kJ in a kcal?

One kilocalorie equals 4.184 kilojoules. Multiply kcal by 4.184 to get kJ.