Calorie

There are several different units of heat, all called the calorie: the International Steam Table calorie, the 15 degree C calorie, the 4 degree C calorie, the mean 1 to 100 degree C calorie, the thermiochemical calorie, and the nutritionists calorie (1000 15 deg C calories).

Of these, the 15 deg. C calorie is what is most commonly meant by calorie in contemporary English text.

A 15 deg C. calorie is a unit of heat. 1 calorie is the amount of heat necessary to raise 1 gram of water from 14.5 to 15.5 ^oC. Typically nutritionists refer to a Calorie (with a capital C), which is really 1000 calories, or 1 kcal.

1 15 deg C. calorie is approximately the equivalent of 4.186 J or 3.968·10^-3 Btu. In many countries kilojoules are used instead.