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How to Convert Calories to Kilojoules (kJ)

The units of energy can be expressed in calories or kilojoules. To convert calories to kilojoules, multiply by a conversion factor as described here.


  • Step 1: Identify unit usage Determine whether the number of calories refers to food calories or scientific calories. Nutritionists and physical scientists use the terms differently.
  • Step 2: Convert food calories Multiply food calories by 4.184 to convert calories to kilojoules.
  • TIP: Food calories are actually scientific kilocalories, which are units of 1,000 scientific calories. Scientific calories are too small to be a meaningful label of food energy.
  • Step 3: Convert scientific calories Multiply scientific calories by 4.184 to convert calories to joules. One joule equal one 1/1000 kilojoules.
  • FACT: One scientific calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius.

You Will Need

  • Energy unit type
  • Calculator

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