Editing Calorie (section)

{{short description|Unit of energy used in nutrition}}
{{Redirect|kcal|text=This article is about the unit of energy. For other uses, see [[KCAL (disambiguation)]] and [[Calorie (disambiguation)]].}}
{{Infobox unit
| name          = calorie
| image         = Energy drink and fast food cheeseburger calorie comparison.jpg
| caption       = A {{convert|24|USfloz|ml|adj=on|order=flip}} [[Monster Energy|Monster]] [[energy drink]] with 330 ''large'' calories
| quantity      = [[energy]]
| symbol        = cal
| units1        = [[SI unit]]s
| inunits1      = 4.184 [[Joule|J]]
}}
The '''calorie''' is a [[unit of energy]] that originated from the [[caloric theory]] of heat.<ref name="morris1992" /><ref name="marsh2020" /> The '''large calorie''', '''food calorie''', '''dietary calorie''', '''kilocalorie''', or '''kilogram calorie''' is defined as the amount of heat needed to raise the [[temperature]] of one [[liter]] of [[water]] by one degree [[Celsius]] (or one [[kelvin]]).<ref name="morris1992" /><ref name="Webster" /> The '''small calorie''' or '''gram calorie''' is defined as the amount of heat needed to cause the same increase in one [[milliliter]] of water.<ref name="Webster" /><ref name="Cambridge" /><ref name="Oxford" /><ref name="morris1992" /> Thus, 1 large calorie is equal to 1,000 small calories.

In [[nutrition]] and [[food science]], the term ''calorie'' and the symbol ''cal'' [[Calorie#Nutrition|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 [[nutritional value|energy value]] of foods in per serving or per weight, recommended [[Dietary Reference Intake|dietary caloric intake]],<ref name=FDA2019/><ref name=NHS2019/> [[metabolic rate]]s, 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;<ref name=conn2019/> however, this convention is often ignored.<ref name=FDA2019/><ref name=NHS2019/><ref name=conn2019/>

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 kcal is not officially part of the [[International System of Units]] (SI), and is regarded as obsolete,<ref name=marsh2020/> having been replaced in many uses by the [[SI derived unit]] of [[energy]], the [[joule]] (J),<ref name=BIPM9th/> or the kilojoule (kJ) for 1000 joules.

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&nbsp;J, and therefore one kilocalorie (one large calorie) is 4184&nbsp;J or 4.184&nbsp;kJ.<ref name=BIPM7th/><ref name=FAO2003/>