There are gram calories and kilogram calories.

It is common to apply metric prefixes to the gram calorie but not to the kilogram calorie.

One kilogram calorie, which equals one thousand gram calories, often appears capitalized and without a prefix (i.e. 'Cal') when referring to "dietary calories" in food.

The large calorie, kilogram calorie, dietary calorie or food calorie (symbol: Cal) approximates the energy needed to increase the temperature of 1 kilogram of water by 1 C. This is exactly 1,000 small calories or about 4.2 kilojoules.