Calorie
unit of energy (4.184 J)
The calorie is a unit of energy that originated from the caloric theory of heat. The small calorie or gram calorie is defined as the amount of heat needed to raise the temperature of one milliliter of distilled water by one degree Celsius (or one kelvin). In the US, the term "Calorie" when used in nutrition refers to a kilocalorie (1 kcal = 1000 cal).
In nutrition and food science, the term calorie and the symbol cal may refer to the large unit or to the small unit in different regions of the world. It is generally used in publications and package labels to express the energy value of foods in per serving or per weight, recommended dietary caloric intake, metabolic rates, etc. Some authors recommend the spelling Calorie and the symbol Cal (both with a capital C) if the large calorie is meant, to avoid confusion; however, this convention is often ignored.
In physics and chemistry, the word calorie and its symbol usually refer to the small unit, the large one being called kilocalorie (kcal). However, the calorie is not part of the International System of Units (SI) and is regarded as obsolete, having been replaced by the SI derived unit of energy, the joule (J).
The precise equivalence between calories and joules has varied over the years, but in thermochemistry and nutrition it is now generally assumed that one (small) calorie (thermochemical calorie) is equal to exactly 4.184 J, and therefore one kilocalorie (one large calorie) is 4184 J or 4.184 kJ.
History
The term "calorie" comes from Latin calor 'heat'. It was first introduced by Nicolas Clément, as a unit of heat energy, in lectures on experimental calorimetry during the years 1819–1824.
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This entry incorporates text from “Calorie” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.