Kilocalories to kilojoules – and kilojoules to kilocalories

Formula

Multiply the value in kilocalories by 4.184 to get kilojoules.
kJ = kcal × 4.184

Multiply the value in kilojoules by 0.23900574 to get kilocalories.
kcal = kJ × 0.23900574

How to convert kilocalories to kilojoules

Type a value in the field above and the result is calculated instantly. Use the arrow button to swap direction, or pick other units from the lists.

Doing it in your head

A rough conversion for when the calculator is not to hand. The error comes last, and it holds in both directions at that order of magnitude.

• Kilocalories to kilojoules: × 4 + 5%. That gives 4.2 instead of 4.184, an error of 0.38%.
• Kilojoules to kilocalories: ÷ 4 − 5%. That gives 0.2375 instead of 0.239006, an error of 0.63%.

About the units

Kilocalories. A kilocalorie is 1,000 calories, exactly 4,184 joules on the thermochemical calorie this conversion is built on. It is the energy unit consumers actually read, but in the EU it may appear only together with the kilojoule: the food information regulation requires both. Nutrition figures are worked out from fixed factors – fat 9 kilocalories per gram, carbohydrate and protein 4, alcohol 7. American labels write “Calories” with a capital C, meaning the same thing. Kilocalorie against calorie is a factor of a thousand.

Kilojoules. A kilojoule is 1,000 joules, since the prefix kilo means 10³, and a legal unit throughout the EU. It is the compulsory energy unit in nutrition labelling: the EU food information regulation requires energy in kilojoules and kilocalories, both. The factors behind the figure sit in the same regulation – fat 37 kJ per gram, carbohydrate and protein 17, alcohol 29. One kilocalorie is 4.184 kilojoules. Because those factors are rounded separately, the two numbers on a pack do not convert exactly into one another.