Kiloelectronvolts to Kilocalories (keV to kcal)

1 kiloelectronvolt equals 3.829294058×10⁻²⁰ kilocalories (rounded).

1 kiloelectronvolt = 3.829294058×10⁻²⁰ kilocalories

How to convert kiloelectronvolts to kilocalories

To convert kiloelectronvolts to kilocalories, multiply the number of kiloelectronvolts by 3.829294058×10⁻²⁰. The factor is rounded to 10 significant digits. To go the other way, multiply kilocalories by 2.611447397×10¹⁹ (rounded).

kilocalories = kiloelectronvolts × 3.829294058×10⁻²⁰

Example: 10 kiloelectronvolts = 3.829294058×10⁻¹⁹ kilocalories.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Kiloelectronvolt (keV)

ScientificCurrent unit

1,000 electronvolts. X-ray photon energies are in this range.

X-rays are the usual home of the keV. Wilhelm Roentgen discovered them on 8 November 1895, and their photon energies span about 100 eV to 100 keV. Photons above roughly 5 to 10 keV count as hard X-rays, while lower ones are soft. Medical diagnostic tubes run at 20 to 150 kilovolts, which sets the highest photon energies of a radiograph at about 20 to 150 keV. One keV is 1.602176634 x 10^-16 J.

Fusion research uses it for temperature. A magnetic confinement plasma at about 15 keV corresponds to roughly 174 million kelvin. Compared with the electronvolt, a kiloelectronvolt is a thousand times larger, so it lies well above the 1 to 10 eV of chemical bonds, yet far below the millions of electronvolts released in nuclear reactions.

1 kiloelectronvolt = 1.602176634×10⁻¹⁶ joules (exactly).

Sources: Wikipedia: X-ray; Wikipedia: Electronvolt

Kilocalorie (kcal)

ScientificTraditional unit (still used in some regions)

1,000 thermochemical calories (4,184 J). The 'Calorie' on food labels in North America.

Marcellin Berthelot separated the gram calorie from the kilogram calorie in 1879, and the American chemist Wilbur Atwater adopted a capital-C Calorie for the large unit in 1887 in a widely read article on the energy in food. Joseph Howard Raymond proposed the term kilocalorie in his 1894 textbook. The two names now describe the same quantity, 1,000 small calories, which at the thermochemical value is 4,184 J or 4.184 kJ.

Food labels carry the unit today, though practice differs by region. North American labels use kilocalories almost exclusively, European labels show kilojoules and kilocalories together under EU Regulation 1169/2011, and Chinese labels give kilojoules only. Typical energy contents are about 9 kcal per gram for fat, about 4 for carbohydrate and protein, and about 7 for alcohol. In electrical terms, 4,184 J works out to about 1.162 watt-hours, since one watt-hour is 3,600 J. NIST also lists a kilocalorie based on the International Table calorie, which is 4,186.8 J.

1 kilocalorie = 4,184 joules (exactly).

Sources: Wikipedia: Calorie (includes kilocalorie); NIST SP 811, Appendix B.8 (energy conversion factors)

Related conversions

See all energy units.