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Both kiloJoules (kJ) and calories (cal) are units that measure energy, usually in the context of nutrition. Luckily, it’s easy to convert between them so you can figure out exactly how much nutritional energy various foods contain.

Method 1
Method 1 of 2:

Changing Kilojoules into Calories

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  1. Nutritional energy is often measured in kilojoules, but you can convert kJ to calories (cal) in a few simple steps. [1]
    • For instance, let’s say you want to convert 5 kJ.
  2. Note that 1 kilojoule is equal to 1,000 joules. So, to convert from kilojoules to joules, multiply the number by 1,000. [2]
    • For example, multiply 5 kJ by 1,000 to equal 5,000 J.
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  3. Note that 1 kJ = 0.239 calories. So, to convert from joules to calories, all you have to do is multiply by 0.239. [3]
    • For example, multiply 5,000 J by 0.239 to get 1,195 cal. Therefore, 5 kJ = 1,195 calories.
  4. Simply divide the number of calories by 1,000 to get the number of kilocalories. [4]
    • For example, divide 1,195 cal by 1,000 to get 1.195 kilocalories. Therefore, 5kJ = 1.195 kcal.
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Method 2
Method 2 of 2:

Converting Back from Calories to Kilojoules

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  1. If you haven’t already, convert the number of calories to kilocalories. [5]
    • For instance, if you have 25 calories, divide this number by 1,000 to get 0.025 kcal.
  2. Note that 1 kcal = 4.184 kJ. So, to convert from kilocalories to kilojoules, multiply by 4.185. [6]
    • For example, multiply 0.025 kcal by 4.184 to get 0.105 kJ. So, 25 calories is equal to 0.105 kilojoules.
  3. If you need to know the number of joules, rather than kilojoules, simply multiply by 1,000. [7]
    • For example, multiply 0.105 kJ by 1,000 to get 105 joules. Therefore, 25 cal = 105 J.
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