A Guide to Energy Units: kcal vs. kJ

Kilocalorie (kcal)

Kilocalorie, commonly abbreviated as kcal, is the prevailing unit of energy measurement used in most countries, including the United States. For example, even though many people use the word “calorie” in the US, in the context of fitness and nutrition they are almost always referring to kilocalories. Scientifically, one kilocalorie represents the amount of energy needed to raise the temperature of one kg of water by one degree Celsius.

Kilojoule (kJ)

Kilojoule, denoted as kJ, is the metric system's counterpart to the kcal. It is commonly used in countries within the EU and is the standard unit for measuring energy. To put it in perspective, 1 kcal is approximately equal to 4.184 kJ. Therefore, kJ values are typically larger than their kcal counterparts for the same amount of energy.

Converting between kcal and kJ

The main difference between kcal and kJ is the measurement scale, but converting between these two units is relatively straightforward. To convert from kcal to kJ, you can use the following formula:‍

Conversely, to convert from kJ to kcal, you would use:

For example, if you have a food item labeled as containing 200 kcal and want to know its equivalent in kJ:

So, 200 kcal is roughly equal to 836.8 kJ.

Understanding the difference between kcal and kJ is essential for anyone conscious of their dietary intake and energy expenditure. While kcal is the standard unit in the United States, kJ is the metric system's widely accepted unit. Knowing how to convert between these units can be particularly helpful when comparing nutritional information or even when you encounter them while traveling.