Calories to Kilojoules Converter

One thermochemical calorie is exactly 4.184 joules, a definition fixed by convention rather than by a water experiment. The food calorie on a nutrition label is a kilocalorie of 4,184 joules.

The small calorie appears in chemistry, physics and heat-capacity problems, where a substance's specific heat is expressed per gram per degree. Nutrition labels use the much larger food calorie instead.

Calories convert to joules by the exact factor 4.184, and kilocalories by 4,184, so no precision is lost in either direction. One kilocalorie is about 4.184 kilojoules, the same amount under another name.

Reading a nutrition label's calorie value as small calories understates the energy by a factor of one thousand. The figure printed there is always the kilocalorie, however it is capitalised or labelled.

The calorie shares its dimension with the kilocalorie, the joule and the kilojoule, and mixing them is the risk. A food label's figure is a kilocalorie, while mechanics and heat problems work in joules and kilojoules.

One kilojoule is exactly 1,000 joules, and the symbol is kJ. It is the joule multiple that food packaging commonly prints, with energy shown in kilojoules beside kilocalories, and chemistry uses it for reaction energies.

Nutrition panels, exercise machines and dietary advice report energy in kilojoules wherever the metric system is used. Materials and fuel data, such as energy content per kilogram, are tabulated in kilojoules as well.

The step from kilojoules to megajoules divides by exactly one thousand, so nothing is lost in the conversion. One kilocalorie equals 4.184 kilojoules, which is how the two columns on a food label correspond.

A reader who compares a kilojoule figure with a kilocalorie figure as though they were the same number will misjudge the energy by more than four times. The label's two columns state one amount in two units.

Kilojoules and kilocalories are the two energy columns on a food label, and the kilojoule figure is the larger number because one kilocalorie is 4.184 kilojoules. Megajoules take over where kilojoule figures become long, as they do for fuels.