Calories versus Kcal - what is the deal?


Have you been using the term “Calories” for, like, ever? Well, you’re probably not alone.

But if you’ve been working on nutrition apps and with nutrition data, you’ve most likely encountered the kcal. For instance, in the Nuwe API or the USDA ingredients database, you’ll get data like:


So if you’re not already aware, this begs the question… what am I dealing with here?

On food packaging you see the term Calories everywhere. In the US, it’s very common to see this:

Whereas in the UK, you are more likely to see this

Here’s the deal, to avoid confusion. Wikipedia says…

The name calorie is used for two units of energy.

The small calorie or gram calorie (symbol: cal) is the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.[1]
The large calorie, kilogram calorie, dietary calorie, nutritionist’s calorie, nutritional calorie, Calorie (capital C)[2] or food calorie (symbol: Cal) is approximately the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. The large calorie is thus equal to 1000 small calories or one kilocalorie (symbol: kcal).[1]

Right, so we have been using small calories right? WRONG! As you can see in the UK example, it’s clear that kcal is used. In the US, the term Calories is actually referring to the unit of kcal, it’s just the naming that differs. Why?

There’s a ridiculous interchanging and miscommunication of the term that is used in common place. If we scroll a bit further down the wikipedia page…

In nutritional contexts, the kilojoule (kJ) is the SI unit of food energy, although the kilocalorie is still in common use.[9] In these contexts, confusingly, the word calorie is very often used for what is actually a kilocalorie of nutritional energy. Sometimes, in an attempt to avoid confusion, it is written Calorie (with a capital “C”) in an attempt to make the distinction, although this is not universal, and is not widely understood.

In attempts to facilitate comparison, specific energy or energy density figures are often quoted, for example “calories per serving” or “kilocalories per 100 g”. Nutritional requirements or intakes are often expressed in calories per day.

Right, so writing “Calorie” with at capital ‘C’ is enough to differentiate it from the “calorie” with a lower case ‘c’. Makes perfect sense :blush:

So, in the nutrition context, when you see Calories or kcal, they are actually referring to the same thing.

There’s a lot more that’s wrong with Food Labelling in general, but this is one area that makes very little sense and needs clarification and a bit of common sense.