On this Wikipedia the language links are at the top of the page across from the article title. The calorie is a unit of energy that originated from the obsolete caloric theory of heat. For historical reasons, two main definitions of “calorie” are in wide use. In nutrition and food science, the term calorie and the symbol cal almost always refers to calories in a brownie square large unit.

This unit was used by U. Joseph Howard Raymond, in his classic 1894 textbook A Manual of Human Physiology. In 1879, Marcellin Berthelot distinguished between gram-calorie and kilogram-calorie, and proposed using “Calorie”, with capital “C”, for the large unit. 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. The joule was the officially adopted SI unit of energy at the ninth General Conference on Weights and Measures in 1948. The alternate spelling calory is considered nonstandard and dated.

The amount of energy equal to exactly 4. The amount of energy required to warm one gram of air-free water from 3. The amount of energy required to warm one gram of air-free water from 14. Experimental values of this calorie ranged from 4. The CIPM in 1950 published a mean experimental value of 4. 1855 J, noting an uncertainty of 0. The amount of energy required to warm one gram of air-free water from 19.

The ‘Thermochemical calorie’ was defined by Rossini simply as 4. 1833 international joules in order to avoid the difficulties associated with uncertainties about the heat capacity of water. It was later redefined as 4. C calorie and the thermochemical calorie.