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Calories vs Kilojoules: How to Read Food Labels Around the World

Updated · 2 min read

Pick up a snack in New York and the label says “Calories”. Pick up the same snack in Sydney and it says “kJ”. In the UK and Europe you may see both. These are all units of energy, and once you know how they relate, comparing foods from any country is easy.

What is a Calorie?

A calorie (lowercase c) is a small unit of energy: about 4.184 joules, the energy needed to warm one gram of water by one degree Celsius. Food energy is so large in these terms that nutrition labels use the kilocalorie (kcal), which is 1,000 calories. Americans call it a Calorie with a capital C, and in everyday use people just say “calories”. So when a label says 200 Calories, that means 200 kilocalories.

What is a kilojoule?

The joule is the official SI unit of energy. One kilocalorie is 4.184 kilojoules (kJ). Australia, New Zealand and several European countries print kilojoules on food labels, and often show kcal as well.

Converting between the two

  • Calories (kcal) to kilojoules: multiply by 4.184. 200 kcal is 837 kJ.
  • Kilojoules to Calories: divide by 4.184. 1,000 kJ is 239 kcal.
  • Mental shortcut: multiply kcal by 4 and add 5 percent, or divide kJ by 4.2.

Use the calories to kilojoules and kilojoules to calories converters for exact results.

How much energy do you need?

Daily requirements depend on age, sex, size and activity. Rough guides often used on labels are:

Reference Calories (kcal) Kilojoules (kJ)
Average adult (Australia reference) 2,080 8,700
US label reference 2,000 8,368
Typical adult woman 1,800 to 2,200 7,500 to 9,200
Typical adult man 2,200 to 2,800 9,200 to 11,700

Tips for reading labels

  • Check the serving size. A bag may contain two or three servings, and the energy figure may refer to only one.
  • Compare foods per 100 g so that you are comparing like with like.
  • Energy per gram is about 4 kcal for protein and carbohydrate, 9 kcal for fat and 7 kcal for alcohol.

The numbers on a food label are estimates, usually accurate to within about 20 percent, so use them as a guide rather than a precise measure.

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