Editing Calorie (section)

==Definitions==
The "small" calorie is broadly defined as the amount of energy needed to increase the temperature of 1&nbsp;gram of water by 1&nbsp;°C (or 1&nbsp;K, which is the same increment, a gradation of one percent of the interval between the melting point and the boiling point of water).<ref name="Cambridge" /><ref name="Oxford" /> The actual amount of energy required to accomplish this temperature increase depends on the atmospheric pressure and the starting temperature; different choices of these parameters have resulted in several different precise definitions of the unit.

{|class=wikitable
|-
! Name !! Symbol !! Conversions !! Definition and notes
|- valign=top
| [[Thermochemistry|Thermochemical]] calorie || cal<sub>th</sub>
| ≡ {{val|4.184|ul=J}}
≈&nbsp;{{val|0.003964|ul=BTU}}
≈&nbsp;{{val|1.162|e=-6|ul=kW.h}}
≈&nbsp;{{val|2.611|e=19|ul=eV}}
| The amount of energy equal to exactly '''4.184&nbsp;J''' ([[joule]]s) and 1&nbsp;kJ ≈ 0.239&nbsp;kcal.<ref name="iso31-4" /><ref name=Rossini/><ref name=lynch1974/><ref name=FAO2003/>{{efn|name=thermochemical}}
|- valign=top
| 4&nbsp;°C calorie || cal<sub>4</sub>
| ≈ 4.204 J
≈&nbsp;<!-- {{convert|4.204|J|BTU|disp=output only}} -->{{val|0.003985|u=BTU}}
≈&nbsp;{{convert|4.204|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.204|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 3.5 to 4.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| 15&nbsp;°C calorie || cal<sub>15</sub>
| ≈ 4.1855 J
≈&nbsp;<!-- {{convert|4.1855|J|BTU|disp=output only}} -->{{val|0.0039671|u=BTU}}
≈&nbsp;{{convert|4.1855|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1855|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 14.5 to 15.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}} Experimental values of this calorie ranged from 4.1852 to 4.1858&nbsp;J. The [[CIPM]] in 1950 published a mean experimental value of 4.1855&nbsp;J, noting an uncertainty of 0.0005&nbsp;J.<ref name="iso31-4" />
|- valign=top
| 20&nbsp;°C calorie || cal<sub>20</sub>
| ≈ 4.182 J
≈&nbsp;<!-- {{convert|4.182|J|BTU|disp=output only}} -->{{val|0.003964|u=BTU}}
≈&nbsp;{{convert|4.182|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.182|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 19.5 to 20.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| Mean calorie || cal<sub>mean</sub>
| ≈ 4.190 J
≈&nbsp;<!-- {{convert|4.19|J|BTU|disp=output only}} -->{{val|0.003971|u=BTU}}
≈&nbsp;{{convert|4.190|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.190|J|eV|disp=output only}}
| Defined as {{frac|100}} of the amount of energy required to warm one gram of air-free water from 0 to 100&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| International [[steam table|Steam Table]] calorie (1929) ||
| ≈ 4.1868 J
≈&nbsp;<!-- {{convert|4.1868|J|BTU|disp=output only}} -->{{val|0.0039683|u=BTU}}
≈&nbsp;{{convert|4.1868|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1868|J|eV|disp=output only}}
| Defined as {{frac|860}} "international" watt hours = {{frac|180|43}} "international" joules exactly.{{efn|The figure depends on the conversion factor between "international joules" and "absolute" (modern, SI) joules. Using the mean international ohm and volt ({{val|1.00049|u=Ω}}, {{val|1.00034|u=V}}),<ref name=iupac/> the "international joule" is about {{val|1.00019|u=J}}, using the US international ohm and volt ({{val|1.000495|u=Ω}}, {{val|1.000330|u=V}}) it is about {{val|1.000165|u=J}}, giving {{val|4.18684}} and {{val|4.18674|u=J}}, respectively.}}
|- valign=top
| International Steam Table calorie (1956) || cal<sub>IT</sub>
| ≡ 4.1868 J
≈&nbsp;<!-- {{convert|4.1868|J|BTU|disp=output only}} -->{{val|0.0039683|u=BTU}}
<nowiki>=</nowiki>&nbsp;{{convert|4.1868|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1868|J|eV|disp=output only}}
| Defined as 1.163&nbsp;mW⋅h = 4.1868&nbsp;J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).<ref name="iso31-4" />
|}
{{notelist|refs=
{{efn|name=thermochemical|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 4.1840 J exactly.{{refn|name=FAO1971}}}}
{{efn|name=pressure|The [[standard atmospheric pressure]] can be taken to be {{val|101.325|u=kPa}}.}}
}}
The two definitions most common in older literature appear to be the ''15&nbsp;°C calorie'' and the ''thermochemical calorie''. Until 1948, the latter was defined as 4.1833 international joules; the current standard of 4.184&nbsp;J was chosen to have the new thermochemical calorie represent the same quantity of energy as before.<ref name="Rossini" />
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