Other units still in use worldwide in some contexts are the kilocalorie per gram (Cal/g or kcal/g), mostly in food-related topics, and watt-hours per kilogram (W⋅h/kg) in the field of batteries.

In some countries the Imperial unit BTU per pound (Btu/lb) is used in some engineering and applied technical fields.

For ionising radiation, the gray is the SI unit of specific energy absorbed by matter known as absorbed dose, from which the SI unit the sievert is calculated for the stochastic health effect on tissues, known as dose equivalent.

[7] In the metric system, the energy unit commonly used on food labels is the kilojoule (kJ) or megajoule (MJ).

In aerobic environments, this typically requires oxygen as an input and generates waste products such as carbon dioxide and water.

Fats contain more carbon-carbon and carbon-hydrogen bonds than carbohydrates or proteins, yielding higher energy density.

A moderate energy density would be 1.6 to 3 calories per gram (7–13 kJ/g); salmon, lean meat, and bread would fall in this category.

Comets have even more energy, typically moving with respect to the Sun, when in our vicinity, at about the square root of two times the speed of the Earth.