Calorie (cal)

Definition

A calorie (cal) is a unit of energy defined as the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius (°C) at 1 atmosphere of pressure. It is not an SI unit but is commonly used in the fields of nutrition and physics. The exact definition is 4.184 joules.

History

The concept of the calorie originated in the early 19th century. Nicolas Clément introduced it in 1824, followed by further refinements by scientists like Jules Henri Poincaré. In 1948, the term "calorie" was standardized in the context of food energy.

Uses

Calories are widely used in nutrition to indicate the energy content of foods. In scientific contexts, they measure heat energy in physics and chemistry. The term is prevalent in countries using the metric system, though it is often replaced by kilojoules (kJ).

Conversions

• 1 calorie = 4.184 joules (exact)
• 1 kilocalorie (kcal) = 1,000 calories (exact)
• 1 Calorie (food calorie) = 1 kilocalorie (exact)

Fun Facts

• A common misconception is that "calorie" and "Calorie" (with a capital C) are the same; in nutrition, 1 Calorie = 1 kilocalorie.
• The average adult requires about 2,000-2,500 calories daily for energy.