Calorie to Kilojoule Converter

A calorie (cal), also called a small calorie or gram calorie, is a unit of energy equal to approximately 4.184 joules. It represents the energy needed to raise the temperature of one gram of water by one degree Celsius at standard atmospheric pressure.

The calorie was defined by French chemist Nicolas Clément in 1824 as a unit for measuring heat. It was widely used in chemistry and physics for calorimetry and thermodynamics before being largely replaced by the joule in scientific applications, though it remains in use for food energy.

Calories are primarily used in chemistry for small-scale energy measurements, in some scientific literature, and occasionally in food and nutrition contexts. However, they've been largely replaced by joules in scientific applications and by kilocalories (food calories) in nutrition.

A kilojoule (kJ) is a unit of energy equal to one thousand joules (10³ J). It's commonly used for measuring food energy content, small-scale mechanical work, and energy in chemical reactions.

The kilojoule became widely adopted in nutrition and food science as many countries moved away from calories to metric energy units. It was officially adopted for food labeling in many countries as part of metrication efforts, providing a more scientifically consistent energy measurement.

Kilojoules are extensively used in food and nutrition labeling, exercise and fitness calculations, chemical reaction energy measurements, and small-scale engineering applications. They're mandatory on food labels in many countries and are standard in sports science and metabolism studies.