Convert Kilocalories to Kilojoules

About converting Kilocalories to Kilojoules

Kilocalories (kcal) and Kilojoules (kJ) are both units of energy, so converting between them is a single multiplication: multiply your Kilocalories figure by 4.184. Ten Kilocalories comes to 41.84 Kilojoules, and a hundred works out at 418.4 Kilojoules.

Rule of thumb: going from Kilocalories to Kilojoules multiplies, so the figure always grows — one Kilocalory is already 4.184 Kilojoules. If your answer came out smaller, you have the conversion the wrong way round.

What is a Kilocalory?

A kilocalorie is a thousand small calories, and it is what people actually mean when they say "calories" about food. Every figure on a nutrition label, every count on a menu board and every target in a diet app is a kilocalorie, even where the label just prints "cal" — a 2,000-calorie day is 2,000 kcal, not 2,000 calories in the physicist’s sense. The convention of capitalising the food unit as Calorie was meant to mark that difference, but it survives mostly in textbooks. Most of the world prints both kJ and kcal on packaging; the United States prints calories alone, which keeps the ambiguity alive.

What is a Kilojoule?

A kilojoule is a thousand joules, the size at which the joule becomes practical for everyday quantities. In Australia and New Zealand it is the primary unit on nutrition labels — food energy is quoted in kilojoules first, with calories relegated to a secondary figure or dropped entirely — so shoppers there think about daily intake in thousands of kilojoules rather than thousands of calories. It is also the working unit of chemistry, where reaction and bond energies are tabulated per mole. European labels print both kJ and kcal, which is why the same packet carries two different numbers for the same food.

To put both in perspective: a plain bagel runs to roughly 250 kilocalories, while a slice of bread carries roughly 300 kilojoules.

The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Kilojoules to Kilocalories converter, or browse all Energy converters.