How do you convert joules to calories?

Use the factor 1 cal = 4.184 J. So calories = joules ÷ 4.184.

What is the difference between cal and kcal?

1 kcal (kilocalorie, sometimes written as Calorie with capital C in nutrition) = 1000 small calories (cal) = 4184 joules.

Can I convert backwards from calories to joules?

Yes. Multiply small calories (cal) by 4.184 to get joules, or multiply kcal by 4184.

Joules to Calories Converter (J ⇄ cal ⇄ kcal)

Converter

Value

From

Results

Joules (J)

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Kilojoules (kJ)

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Calories (cal)

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Kilocalories (kcal)

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Steps

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Joule vs calorie: the definition

A joule (J) is the SI unit of energy. A calorie (cal) in this context is the thermochemical small calorie, defined as:

1 cal = 4.184 J

1 kcal = 1000 cal = 4184 J

Food labels usually use kcal but write “Calories” with a capital C.

Formulas

J → cal: \( \text{cal} = \dfrac{\text{J}}{4.184} \)

J → kcal: \( \text{kcal} = \dfrac{\text{J}}{4184} \)

cal → J: \( \text{J} = \text{cal} \times 4.184 \)

kcal → J: \( \text{J} = \text{kcal} \times 4184 \)

kJ → J: \( \text{J} = \text{kJ} \times 1000 \)

FAQ

Does it use 4.184 or 4.2?

This tool uses the more precise 4.184 J per cal (thermochemical). Some textbooks round to 4.2 J, which is OK for quick physics problems but less exact.

Can I convert kJ directly to kcal?

Yes: first convert kJ → J (×1000) then J → kcal (÷4184). The calculator performs both steps at once.