This article is about the unit of energy. For its use in nutrition and food labelling regulations, see the article on food energy. Nutrition (also called nourishment or aliment) is the provision to cells and Organisms of the materials necessary (in the form of food to support This article is based around UK Law and some European Union regulations and therefore is region sensitive Food energy is the amount of Energy in food that is available through Digestion.

The calorie is a pre-SI unit of energy, in particular heat. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature ^[1] In most fields, its use is archaic, and the SI unit of energy, the joule, has become accepted. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity However, it remains in common use as a unit of food energy. Food energy is the amount of Energy in food that is available through Digestion. It was first defined by Professor Nicolas Clément in 1824 as a kilogram-calorie, and this definition entered French and English dictionaries between 1841 and 1867. Nicolas Clément (1779 Dijon - 1842 was a French physicist and chemist. Etymology: French calorie, from Latin calor (heat).

The unit calorie has historically been used in two major alternate definitions that differ by a factor of 1000:

• The small calorie, gram calorie, or calorie (symbol: cal) is the amount of heat (energy) required to raise the temperature of one gram of water by 1 °C. The Celsius Temperature scale was previously known as the centigrade scale.

• The large calorie, kilogram calorie, kilocalorie (symbol: kcal), or Calorie (capital C) is the amount of heat (energy) needed to increase the temperature of one kg of water by 1 °C, exactly 1000 small calories, or about 4. 184 kJ. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity

The second form is the one commonly used to express food energy. Food energy is the amount of Energy in food that is available through Digestion. Its most common name is calorie; kilocalorie is sometimes used, more often in the symbol "kcal" than in the spelled out word.

Apart from these two major alternate definitions, there exist also minor variants of the definition of this unit, which differ in the exact experimental conditions used, most notably the start temperature of the water (see section below).

The factors used to convert measurements in calories to their equivalents in joules are numerically equivalent to expressions of the specific heat capacity of water in SI units. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity Water is a common Chemical substance that is essential for the survival of all known forms of Life. See "Versions" below for an explanation of the units.

1 cal_IT = 4. 1868 J (1 J = 0. 23885 cal_IT) (International Steam Table calorie, 1956)

1 cal_th = 4. 184 J (1 J = 0. 23901 cal_th) (Thermochemical calorie)

1 cal₁₅ = 4. 18580 J (1 J = 0. 23890 cal₁₅) (15°C calorie)

Versions

The energy needed to increase the temperature of a gram of water by 1 degree Celsius depends on the starting temperature and is difficult to measure precisely. The Celsius Temperature scale was previously known as the centigrade scale. Accordingly, there have been several definitions of the calorie:

• Thermochemical calorie (cal_th): 4. In Thermodynamics and Physical chemistry, thermochemistry is the study of the Heat evolved or absorbed in Chemical reactions Thermochemistry 184 J exactly. ^[1]
• 15 °C calorie (cal₁₅): the amount of energy required to warm 1 g of air-free water from 14. 5 °C to 15. 5 °C at a constant pressure of 101. 325 kPa (1 atm). The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm Experimental values of this calorie ranged from 4. 1852 J to 4. 1858 J. The CIPM in 1950 published a mean experimental value of 4. The International Committee for Weights and Measures is the English name of the Comité international des poids et mesures ( CIPM, sometimes written in English 1855 J, noting an uncertainty of 0. 0005 J. ^[1]
• 20 °C calorie: the amount of energy required to warm 1 g of air-free water from 19. 5 °C to 20. 5 °C at a constant pressure of 101. 325 kPa (1 atm). The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm This is about 4. 182 J.
• 4 °C calorie: the amount of energy required to warm 1 g of air-free water from 3. 5 °C to 4. 5 °C at a constant pressure of 101. 325 kPa (1 atm). The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm
• Mean calorie: 1/100 of the amount of energy required to warm 1 g of air-free water from 0 °C to 100 °C at a constant pressure of 101. 325 kPa (1 atm). The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm This is about 4. 190 J
• International Steam Table Calorie (1929): (1/860) W h = (180/43) J exactly. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. This is approximately 4. 1868 J.
• International Steam Table Calorie (1956) (cal_IT): 1. 163 mW h = 4. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 1868 J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956). ^[1]
• IUNS calorie: 4. 182 J exactly. This is a ratio adopted by the Committee on Nomenclature of the International Union of Nutritional Sciences. ^[2]

The two perhaps most popular definitions used in older literature are the "15 °C calorie" and the "thermochemical calorie". Since the many different definitions are a source of confusion and error, all calories are now deprecated in favour of the SI unit for heat and energy: the joule (J). In Computer software standards and documentation the term deprecation is applied to Software features that are superseded and should be avoided The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity

References

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