Calories to Kilojoules Converter

To convert a measurement in calories to kilojoules, multiply the value by 0.004184. The conversion factor comes from the relationship between both units and the joule.

For example, to convert 5 cal to kilojoules: 5 × 0.004184 = 0.02092 kJ.

A calorie (small calorie) is the energy needed to raise the temperature of one gram of water by one degree Celsius, defined as exactly 4.184 joules. The calorie originated in early-19th-century thermodynamics. The thermochemical calorie, fixed at exactly 4.184 J, is the modern standard, though it is often confused with the larger food Calorie (kilocalorie).

Common uses of calories include: Chemistry and thermodynamics; Heat-of-reaction measurements; Physics heat-transfer problems; Historical energy references.

A kilojoule equals 1,000 joules and is the standard metric unit for expressing food energy on nutrition labels in most of the world. As metric countries adopted SI units for food labeling, the kilojoule replaced the food calorie on packaging in regions such as Australia, New Zealand, and the European Union (shown alongside kcal).

Common uses of kilojoules include: Food energy on nutrition labels; Dietary and exercise energy tracking; Chemical reaction energy (enthalpy); Battery and mechanical energy specs.

Here are some common values converted:

1 cal = 0.004184 kJ 5 cal = 0.02092 kJ 10 cal = 0.04184 kJ 50 cal = 0.2092 kJ 100 cal = 0.4184 kJ