Calories

A calorie is a unit of measurement for energy. Calorie is French and derives from the Latin calor (heat). In most fields, it has been replaced by the joule, the SI unit of energy. However, the kilocalorie or Calorie (capital "C") remains in common use for the amount of food energy.
Definitions for calorie fall into 3 classes:
The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.184 joules.
The large calorie or kilogram calorie approximates the energy needed to increase the temperature of 1 kg of water by 1 °C. This is about 4.184 kJ, and exactly 1000 small calories.
The mega calorie or ton calorie[citation needed] approximates the energy needed to increase the temperature of 1 ton of water by 1 °C. This is about 4.184 MJ, and exactly 1000 large calories.
In scientific contexts, the name "calorie" refers strictly to the gram calorie, and this unit has the symbol cal. SI prefixes are used with this name and symbol, so that the kilogram calorie is known as the "kilocalorie" and has the symbol kcal. In non-scientific contexts the kilocalorie is often referred to as a Calorie (capital "C"), or just a calorie, and it has to be inferred from the context that the small calorie is not intended.
The conversion factor between calories and joules is numerically equivalent to the specific heat capacity of liquid water (in SI units).
1 calINT = 4.1868 J (1 J = 0.23885 calIT)
1 calth = 4.184 J (1 J = 0.23901 calth)
1 cal15 = 4.18580 J (1 J = 0.23890 cal15)