calories

The calorie is a unit of energy.
There are actually two units with the name that have been widely used. The small calorie or gram calorie (usually denoted cal) is the amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius (or one kelvin). The large calorie, food calorie, or kilocalorie (Cal or kcal) is the amount of heat needed to cause the same increase on one kilogram of water. Thus, 1 kcal = 1000 cal.
The large calorie is sometimes written Calorie (with a capital C) to distinguish from the other unit. However, this convention cannot be relied upon, since it is often ignored – especially in non-technical publications.Although both units are related to the metric system, they have been considered obsolete, or deprecated, in scientific usage, since the adoption of the SI system. The SI unit of energy is the joule, with symbol "J" (since 1889); one small calorie is now defined as exactly 4.184 J, and one large calorie is 4184 J.
However, the two units are still used occasionally in technical work, and the large calorie is still widely used in nutrition. In most countries, the labels of industrialized food products are required to indicate the nutritional energy value in (large) calories per serving or per weight.

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