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.

It is defined as one kilocalorie of energy (1000 thermochemical gram calories) per one mole of substance, that is, per Avogadro's number of particles.

The small calorie or gram calorie (symbol: cal) approximates the energy needed to increase the temperature of 1 gram of water by 1 C. This is about 4.2 joules.