A calorie is a unit of energy. In nutrition and everyday language, calories refer to energy consumption through eating and drinking and energy usage through physical activity. For example, an apple may have 80 calories, while a 1 mile walk may use up about 100 calories.
There are two types of calories:
(1) A small calorie (symbol: cal) - 1cal is the amount of energy required to raise one gram of water by one degree Celsius.
(2) A large calorie (symbol: Cal, kcal) - 1Cal is the amount of energy required to raise one kilogram of water by one degree Celsius.
1 large calorie (1kcal) = 1,000 small calories.
Most people associate calories just with food and drink, but anything that contains energy has calories. One ton of coal contains the equivalent in energy of 7,004,684,512 calories.
The terms large calorie and small calorie can be confusing, and to add further confusion, are often mistakenly used interchangeably. This article focuses on calories associated with foods, drinks and human energy expenditure (our burning up of energy).
According to Medilexicon's medical dictionary, a Calorie is "A unit of heat content or energy. The amount of heat necessary to raise 1 g of water from 14.5-15.5°C (small calorie). Calorie is being replaced by joule, the SI unit equal to 0.239 calorie." Shop online.
The calories included in food labels are, infact, kilocalories - units of 1,000 small calories. Therefore, a 250-calorie chocolate bar is actually 250,000 calories.