Calories

The standard unit of heat energy is the calorie (cal), defined as the amount of heat energy necessary to raise the temperature of 1 g of water 1 degree, from 15 °C to 16 °C. This unit is also called the gram calorie, small calorie, or standard calorie. The unit commonly used in physiology and medicine is the Calorie (kilocalorie; kcal), which equals 1000 cal.