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Calories to Kilojoules

For reading an Australian or European nutrition label.

Inputs
kcal

The number of calories (kcal) to convert.

Kilojoules
8,368kJ
As a share of a 2,000 kcal day
100.0%
In joules
8,368,000J
100 kcal
418.4kJ
500 kcal
2,092kJ
2,000 kcal
8,368kJ
2,500 kcal
10,460kJ
kJ = kcal × 4.184

1 kcal = 4.184 kJ

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One food calorie is 4.184 kilojoules. A 2,000 calorie daily intake is 8,368 kJ, and Australian labels commonly round the reference to 8,700 kJ.

How to use Calories to Kilojoules Converter

  1. Enter the calories. From the label, where they may be written as kcal or Cal.
  2. Read the kilojoules. With the share of a typical day shown alongside.

About converting calories to kilojoules

The calorie and the kilojoule measure the same thing and belong to different systems. The joule is the SI unit of energy and the calorie is a legacy unit defined originally as the heat needed to raise one gram of water by one degree Celsius — a definition that turns out to depend slightly on the starting temperature, which is why the modern thermochemical calorie is simply fixed at exactly 4.184 joules by convention. Food labelling is where most people meet the conversion, and there is an unfortunate naming collision underneath it. The calorie on a nutrition label is a kilocalorie, a thousand of the unit a physicist means. It is variously written kcal, Cal with a capital C, or just calories, all referring to the same larger quantity. This is why an energy bar showing 250 calories is not remotely comparable to a chemistry figure quoted in calories, and why kJ avoids the ambiguity entirely. Which unit appears is a matter of jurisdiction. Australia and New Zealand mandate kilojoules, the European Union requires both kJ and kcal, and the United States uses calories alone. The Australian reference intake of 8,700 kJ, equivalent to about 2,079 calories, exists for calculating the percentage figures on packaging rather than as advice — actual requirements vary enormously with body size, composition and activity, which is what a personal estimate is for.

Frequently asked questions

Is a food calorie the same as a calorie?
No, and the naming is genuinely bad. A food Calorie is a kilocalorie — a thousand of the physics calorie. Labels write it as kcal, Cal or simply calories interchangeably, all meaning the same larger unit.
Why do labels use kilojoules?
Because the joule is the SI unit of energy and the calorie is not. Australia and New Zealand require kilojoules, the EU requires both, and the United States uses calories alone. The underlying quantity is identical.
What is the Australian 8,700 kJ figure?
The reference daily intake used on Australian labelling, equivalent to about 2,079 calories. It is a labelling reference for percentage calculations rather than a personal recommendation, and individual needs vary widely around it.
Where does 4.184 come from?
It is the thermochemical calorie, defined as exactly 4.184 joules. The original definition — the energy to raise one gram of water by one degree — varies slightly with temperature, so the exact value was fixed by convention.

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