A calorie is a unit of energy. Specifically, a "small" calorie (cal) is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius at standard atmospheric pressure. The "large" calorie, also known as a kilocalorie (kcal) or Calorie with a capital C, is the amount of energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius. This large calorie is the unit commonly used in nutrition to express the energy content of food and drink
. In terms of energy equivalence, one small calorie equals exactly 4.184 joules, so one kilocalorie (large calorie) equals 4184 joules
. Food labels typically use kilocalories but often just say "calories," so a 250-calorie chocolate bar actually contains 250,000 small calories
. Calories are essential because they provide the energy the body needs to function, including physical activity and basic metabolic processes
. The number of calories a person needs daily varies depending on factors like age, sex, weight, height, and activity level
. In summary:
- Small calorie (cal): energy to raise 1 g water by 1°C
- Large calorie / kilocalorie (kcal or Cal): energy to raise 1 kg water by 1°C = 1000 small calories
- Used in nutrition to measure energy in food
- 1 cal = 4.184 joules; 1 kcal = 4184 joules
- Caloric intake is vital for bodily energy needs and varies per individual
