Kilojoules to Calories Converter
Type into either box and the other updates instantly. Food labels in the EU, UK, Australia and New Zealand are usually in kilojoules, while the US uses kilocalories.
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The Conversion Factor
One kilocalorie equals 4.184 kilojoules, so the arithmetic is simple in both directions:
- kJ to kcal: divide by 4.184 (or multiply by 0.239)
- kcal to kJ: multiply by 4.184
- Shortcut approximation: 1 kcal ≈ 4.2 kJ, which is accurate enough for reading a label at a glance
The factor comes from the thermochemical definition: one calorie is the energy needed to raise 1 g of water by 1 °C, and the modern calorie used in nutrition is the large calorie (kilocalorie) defined as exactly 4.184 joules.
Calories, kcal and kJ: Clearing Up the Vocabulary
A “Calorie” on a nutrition label, with a capital C, is a kilocalorie — 1,000 small calories. That is why a banana is described as having about 105 Calories rather than 105,000. Kilojoules are simply the same energy expressed in the SI unit, and the conversion between the two is exact and unambiguous, unlike almost every other number in nutrition.
Common Conversions
- 100 kcal = 418 kJ
- 250 kcal = 1,046 kJ (a typical chocolate bar)
- 500 kcal = 2,092 kJ (a large meal)
- 1,000 kcal = 4,184 kJ
- 2,000 kcal = 8,368 kJ (a commonly used daily reference intake)
- 2,500 kcal = 10,460 kJ
Reading the other way, a snack labelled 600 kJ is about 143 kcal, and 1,000 kJ is about 239 kcal.
Where Rounding and Labels Can Mislead
- Label rounding rules differ by country. The EU permits rounding to the nearest 1 kJ and 1 kcal, so converted values can differ by a few units from the manufacturer’s own figure.
- Energy values are calculated, not measured. Most labels use Atwater factors — 4 kcal/g for protein and carbohydrate, 9 kcal/g for fat, 7 kcal/g for alcohol — which are averages and can differ from the true metabolisable energy of a specific food.
- Fibre and polyols are counted differently in different regulatory systems, so two labels for the same product can legitimately disagree.
- “Net” or “available” carbohydrate figures change the calculated energy without changing the conversion factor.
None of this affects the maths on this page: the unit conversion is exact. It affects how much you should trust the last digit of any label. To put a converted figure into context, our calorie calculator estimates daily energy needs, and the macro calculator turns them into protein, carbohydrate and fat.
Frequently Asked Questions
Is a kilojoule the same as a calorie?
No. A kilojoule is an SI unit of energy; a kilocalorie is the older nutrition unit. One kilocalorie equals 4.184 kilojoules.
Why do Australian and European labels use kJ?
Both jurisdictions require kilojoules, with kilocalories often shown alongside. The US and Canada use kilocalories, which is why the same product can look like it contains different numbers on different packaging.
Can I just divide by 4 instead of 4.184?
You can for a rough estimate, but it overestimates the calorie content by about 4.5 %. Dividing by 4.2 is closer for mental arithmetic.