The calorie was first introduced by Nicolas Clément, as a unit of heat energy, in lectures during the years 1819–1824. This was the “large” calorie, viz. modern kilocalorie.[3][6] The term entered French and English dictionaries between 1841 and 1867. It comes from Latin calor ‘heat’.

The “small” calorie (modern calorie) was introduced by Pierre Antoine Favre (Chemist) and Johann T. Silbermann (Physicist) in 1852. In 1879, Marcellin Berthelot distinguished between gram-calorie (modern calorie) and kilogram-calorie (modern kilocalorie).[6] Berthelot also introduced the convention of capitalizing the kilogram-calorie, as Calorie.

The use of the kilogram-calorie (kcal) for nutrition was introduced to the American public by Wilbur Olin Atwater, a professor at Wesleyan University, in 1887.[3]

The modern calorie (cal) was first recognized as a unit of the cm-g-s system (cgs) in 1896,[6] alongside the already-existing cgs unit of energy, the erg (first suggested by Clausius in 1864, under the name ergon, and officially adopted in 1882).

Already in 1928 there were serious complaints about the possible confusion arising from the two main definitions of the calorie and whether the notion of using the capital letter to distinguish them was sound.[7] Use of the calorie was officially deprecated by the ninth General Conference on Weights and Measures, in 1948.[8]

The alternate spelling calory is archai