Kilocalories to Electronvolts (kcal to eV)

1 kilocalorie equals 2.611447397×10²² electronvolts (rounded).

1 kilocalorie = 2.611447397×10²² electronvolts

How to convert kilocalories to electronvolts

To convert kilocalories to electronvolts, multiply the number of kilocalories by 2.611447397×10²². The factor is rounded to 10 significant digits. To go the other way, multiply electronvolts by 3.829294058×10⁻²³ (rounded).

electronvolts = kilocalories × 2.611447397×10²²

Example: 10 kilocalories = 2.611447397×10²³ electronvolts.

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

About these units

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)

Electronvolt (eV)

ScientificCurrent unit

Exactly 1.602176634×10⁻¹⁹ joules, the energy gained by an electron moving through one volt. Used in atomic and particle physics.

Particle physicists adopted this unit because a charged particle crossing a voltage V gains energy qV, so an electron accelerated through one volt in a vacuum gains exactly one electronvolt. Since the 2019 revision of the SI, the elementary charge is fixed, which makes 1 eV exactly 1.602176634 x 10^-19 J. The NIST appendix page still shows a rounded, non-exact value, reflecting the time before this redefinition. The unit is not part of the SI itself.

It suits the atomic world. Visible photons carry roughly 1.65 to 3.26 eV, green light at 532 nm is about 2.33 eV, and ionising hydrogen needs 13.6 eV. Molecular bonds are on the order of 1 to 10 eV each, and thermal motion at 20 degrees Celsius corresponds to about 0.025 eV. Particle masses are also quoted in eV/c squared, so the proton is about 938 million of them. Larger multiples such as keV, MeV and GeV extend the scale upward.

1 electronvolt = 1.602176634×10⁻¹⁹ joules (exactly).

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

Related conversions

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