Calories, Kilocalories and Kilojoules on Food Labels
The Calorie you count is a thousand times bigger than the calorie in a physics textbook. Here is how the units line up.
23 March 2026 · 5 min read · Health
Food labelling contains one of the most widespread unit inconsistencies in daily life.
Two calories
- calorie (cal) — energy to heat 1 g of water by 1 °C. Roughly 4.184 joules.
- Calorie (kcal) — a thousand of those. This is the "calorie" on every nutrition label.
A chocolate bar listed at "250 calories" contains 250 kilocalories, or 250,000 physics calories. The capital C convention exists but is inconsistently applied, so most countries now print kcal explicitly.
Kilojoules
The SI unit is the joule. Australia, New Zealand and much of the EU print kilojoules alongside or instead of kcal.
1 kcal = 4.184 kJ kJ ÷ 4.184 = kcal
| kJ | kcal |
|---|---|
| 500 | 120 |
| 1,000 | 239 |
| 2,000 | 478 |
| 8,700 | 2,079 |
Australia's reference daily intake is 8,700 kJ, which is why that number appears everywhere on Australian packaging. It corresponds to roughly 2,080 kcal. Convert with the kilojoules to kilocalories converter.
Per 100 g versus per serving
EU labels must show energy per 100 g, which makes products directly comparable. US labels show per serving, and the serving size is chosen by the manufacturer — a bag of crisps may declare 2.5 servings. Always check the denominator before comparing two products.
The numbers are estimates
Label figures come from the Atwater system: 4 kcal per gram of protein, 4 for carbohydrate, 9 for fat, 7 for alcohol, 2 for fibre. It is an average model, not a measurement of the specific food, and regulators allow a tolerance of around 20%. Treat calorie counts as a useful comparison tool, not a precise instrument.
Related conversions
This article is for general information and is not medical advice. Always confirm readings and decisions with a qualified healthcare professional. About accuracy