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Food Calorie to Joule Converter

Enter an energy value and pick a direction to convert between food Calories and joules.

Result

1,046,000 J
1 kcal = 4,184 J
1 J = 0.00023901 kcal

How it is calculated

The conversion uses one fixed factor, 1 kcal = 4184 J. Going from food Calories to joules, J = kcal × 4184; going back, kcal = J ÷ 4184. The direction setting picks which of the two is used (kcal to J is the default). The value must be greater than zero; zero and negative numbers give no result.

Joules are shown as whole numbers and kilocalories with up to six decimals, together with the factor in both directions (1 J = 0.00023901 kcal). To get kilojoules, which many labels outside the US print, divide the joule result by 1000. The tool converts the unit only: it does not know what a food contains, so the number you enter must already be the energy for the portion you eat.

Worked example

A snack bar is labelled 250 kcal. In the kcal to J direction: 250 × 4184 = 1,046,000 J, which is 1,046 kJ. Going the other way as a check, 1,046,000 ÷ 4184 = 250 kcal. For a small value in the opposite direction, 1,000,000 J ÷ 4184 gives 239.005736 kcal, shown with six decimals.

Try this example →

Common mistakes

  • Confusing the food Calorie (kcal) with the small calorie (cal). A label's 250 Calories is 250,000 small calories, so converting as if it were 250 cal would give a result 1000 times too small.
  • Reading the answer in joules when a label uses kilojoules. 1,046,000 J is 1,046 kJ; mixing the two prefixes is a factor-of-1000 error.
  • Choosing the wrong direction. If you enter 1046 meaning kJ and leave kcal to J selected, it is read as 1046 kcal.
  • Entering 0 or a negative number to test the tool. Only positive values are accepted, so the result stays empty.
  • Assuming the factor changes between foods or with temperature. The tool always uses exactly 4184 J per kcal, so it is a unit conversion, not an estimate of absorbed energy.

About this calculator

The “Calorie” printed on food labels (capital C, formally a kilocalorie or kcal) is a unit of energy from an older thermochemical system, while the joule is the SI unit of energy used throughout physics, chemistry and most of the world outside US food labeling. The conversion is fixed and exact by definition: 1 kcal = 4184 J (based on the thermochemical calorie of exactly 4.184 J, scaled up a thousand times).

Nutrition scientists, exercise physiologists and anyone reading food energy content in a country that labels in kilojoules — most food labels outside the US show both kcal and kJ — rely on this conversion to reconcile the two systems, since a food energy value is meaningless without knowing which unit it’s expressed in.

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Comments (1)

  • Editorial team

    For a quick mental check, multiply kilocalories by about 4.2 to get kilojoules: 100 kcal is close to 420 kJ. Packaged food in many countries prints both numbers, and because each is rounded separately the printed pair may differ slightly from an exact 4,184 conversion. Do you usually convert label values to kilojoules, or go the other way for a sports or lab figure?

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