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Calories to Kilojoules Converter

Convert food calories to kilojoules instantly, with a reference table for exercise, meals and daily targets.

Calories to KJ Converter

1 kcal = 4.18 kJ

Multiply calories by 4.184 to get kilojoules.

The link carries the values you entered, so whoever opens it sees the same result. Nothing is stored on our side — the numbers travel in the link itself.

Calories to kilojoules reference table

The conversions people look up most often, rounded to 2 decimal places.

Common calories to kilojoules conversions
Calorie (kcal)Kilojoule (kJ)
50 kcal209.2 kJ
100 kcal418.4 kJ
200 kcal836.8 kJ
250 kcal1,046 kJ
400 kcal1,673.6 kJ
500 kcal2,092 kJ
800 kcal3,347.2 kJ
1,000 kcal4,184 kJ
1,500 kcal6,276 kJ
2,000 kcal8,368 kJ
2,500 kcal10,460 kJ
3,000 kcal12,552 kJ

How the calories to kj converter calculation works

A food calorie is exactly 4.184 kilojoules:

kilojoules = calories (kcal) × 4.184

The joule is the SI unit of energy; the calorie is a survival from an older system, defined as the energy needed to raise one gram of water by one degree Celsius. The 4.184 figure is the mechanical equivalent of heat, measured by Joule in the 1840s and now fixed by definition.

Everything below uses the food calorie (kcal), which is what appears on a label.

Meals and targets:

  • 500 kcal → 2,092 kJ
  • 2,000 kcal → 8,368 kJ — the US daily reference
  • 2,500 kcal → 10,460 kJ
  • 3,000 kcal → 12,552 kJ

Exercise, which is where the number is most often misread:

  • 30 minutes of brisk walking, ~150 kcal → 628 kJ
  • An hour of cycling, ~500 kcal → 2,092 kJ
  • A marathon, ~2,600 kcal → 10,878 kJ

A useful piece of perspective: a pound of body fat stores roughly 3,500 kcal, or 14,644 kJ. That is why a 500 kcal daily deficit is the standard advice for losing about a pound a week — and why an hour of exercise, at 400–600 kcal, does not offset a large meal.

Why some countries lead with kilojoules. Australia and New Zealand mandate kJ on labels because it is the SI unit and avoids the calorie/kilocalorie ambiguity entirely. There is no "kilo-kilojoule" confusion to have.

Frequently asked questions

How do I convert calories to kilojoules?

Multiply the number of calories by 4.184 to get kilojoules.

How many kilojoules are in 400 kcal?

400 kcal equals 1673.60 kJ. The reference table on this page lists the other values people look up most often.

How do I convert kilojoules back to calories?

Divide the number of kilojoules by 4.184, or use the swap control on the converter above.

Is this conversion exact?

Yes. The factor is fixed by international definition rather than measured, so the conversion is exact - only the displayed rounding limits precision.

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