Convert kilocalories to kilojoules

The formula

kilojoules = kilocalories × 4.184

kilocalories to kilojoules — quick reference

The "calories" on a food label are already kilocalories

A biscuit listed at 250 calories contains 250 kilocalories, which is 250,000 of the small calories used in chemistry. The food industry dropped the prefix decades ago and never restored it, so the everyday word and the scientific unit differ by a factor of a thousand. The number to enter here is the one printed on the label, not that number with three zeros added.

The relationship to joules is fixed by definition rather than measured: 1 kcal is exactly 4.184 kJ under the thermochemical definition. That is why the result is exact rather than approximate, and why a European label showing 1046 kJ beside 250 kcal is not rounding loosely — it is the same quantity written out twice.

Why an American label needs converting at all

EU regulation requires both kJ and kcal on packaged food, with kilojoules listed first, and Australia and New Zealand go further by using kilojoules almost exclusively. American labels carry kcal alone. The same product therefore appears with completely different numbers on either side of the Atlantic while nothing about the food has changed.

Recalculating a nutrition panel is the usual reason to do this: an imported recipe, an app that expects kilojoules, or a daily target set in one system against food labelled in the other. The reference intake of 2,000 kcal works out at 8,368 kJ, which is why EU labels quote 8400 kJ as the round figure rather than anything ending in two zeros.

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