The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule. However, in many countries it remains in common use as a unit of food energy.
Definitions of a calorie fall into two classes:
In an attempt to avoid confusion the large calorie is sometimes written as Calorie (with a capital C). This convention, however, is not always followed, and not explained to the average person clearly (and is sometimes impossible). Whether the large or small calorie is intended often must be inferred from context. When used in scientific contexts, the term calorie refers to the small calorie.
The gram calorie, however, is a very small a unit for use in nutritional contexts. Larger units are therefore used. The kilocalorie (symbol: kcal), being 1000 small calories, is one such unit. The large…