1. Amount of heat required to raise the temperature of one gram of water by 1°C. It equals 4.18 joules or about 0.004 British thermal units (Btu). Also called gram calorie or small calorie.
2. Unit of energy-producing potential of a food (commonly shown as calorie on the nutrition label of the item) is actually a kilocalorie equal to 1,000 small calories amount of heat required to raise the temperature of one kilogram of water by 1°C. It equals 4.18 kilojoules or about 4 British thermal units (Btus). Also called food calorie, kilogram calorie, large calorie, or nutrition calorie.