Mark S. Frey
guide to inversion tables
a measure of the amount of energy in food
In spite of its non-official status, the large calorie is still widely used as a unit of food energy. The small calorie is also often used for measurements in chemistry, although the amounts involved are typically recorded in kilocalories. The calorie was first defined by Nicolas Clément in 1824 as a unit of heat, and entered French and English dictionaries between 1841 and 1867. The word comes from Latin calor meaning "heat".
Although these units are part of the metric system, they have been superseded in the International System of Units by the joule. One small calorie is approximately 4.2 joules (so one large calorie is about 4.2 kilojoules). The factor used to convert calories to joules at a given temperature is numerically equivalent to the specific heat capacity of water expressed in joules per kelvin per gram or per kilogram.