What Is the Calories to Kilojoules Calculator?
This calculator converts energy measured in calories (more precisely, kilocalories or kcal, the unit printed on food labels) into kilojoules (kJ). Many countries — including the UK, Australia, and across the EU — list food energy in kilojoules, while others use calories. This tool bridges the two using the standard thermochemical conversion.
How to Use It
Type the number of calories (kcal) you want to convert into the input box and read the kilojoule result instantly. For example, a snack bar listed as 250 calories converts to just over 1,000 kJ. You can enter whole numbers or decimals.
The Formula Explained
The conversion is a simple multiplication:
$$\text{kJ} = \text{kcal} \times 4.184$$
One kilocalorie (the "Calorie" on nutrition labels) equals exactly 4.184 kilojoules under the thermochemical definition. So to go from calories to kilojoules you multiply by 4.184; to reverse it, divide kilojoules by 4.184.
Worked Example
Suppose a meal contains 500 kcal. Multiply: $$500 \times 4.184 = 2{,}092 \text{ kJ}$$ That meal therefore provides 2,092 kilojoules of food energy.
FAQ
Is a calorie the same as a kilocalorie? On food labels, "Calorie" (capital C) means kilocalorie. This calculator treats your input as kilocalories, which is what nutrition labels use.
Why 4.184 and not 4.2? \(4.184\) is the precise thermochemical conversion factor. Some sources round to \(4.2\) for quick estimates, but \(4.184\) is more accurate.
How do I convert kilojoules back to calories? Divide the kilojoule value by 4.184. For example, \(2{,}092 \div 4.184 = 500\) kcal.
