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Calorie - The amount of heat needed to raise one kilogram of water by 10-degree Celsius. Term calorie is also used as a measure of food energy.

The calorie is a unit of energy and 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.