Electronvolts to Calories (eV to cal)

1 electronvolt equals 3.829294058×10⁻²⁰ calories (rounded).

1 electronvolt = 3.829294058×10⁻²⁰ calories

How to convert electronvolts to calories

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

calories = electronvolts × 3.829294058×10⁻²⁰

Example: 10 electronvolts = 3.829294058×10⁻¹⁹ calories.

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

About these units

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)

Calorie (cal)

ScientificTraditional unit (still used in some regions)

The thermochemical calorie: exactly 4.184 joules, the energy to raise one gram of water by one degree Celsius. Not the same as the food Calorie, which is a kilocalorie.

Latin calor, meaning heat, supplied the name. Nicolas Clement used it in lectures on heat engines between 1819 and 1824, and by 1852 Pierre Favre and Jean Silbermann applied it to the small unit based on a single gram of water warmed by one degree Celsius. Because the specific heat of water varies slightly with temperature, early calories differed from one laboratory to the next. A mean value near 4.1855 J was published for the 15 degree calorie in 1950, with an uncertainty of 0.0005 J.

Chemists settled the matter by definition. The thermochemical calorie is exactly 4.184 J, which is the figure used here, and NIST lists it with that exact value. The calorie is not an SI unit and is regarded as obsolete, since the ninth General Conference on Weights and Measures in 1948 preferred the joule for heat. One thousand of these calories make a kilocalorie, the larger unit used for food, and a slightly larger calorie, the International Table version of 4.1868 J, is used in steam tables.

1 calorie = 4.184 joules (exactly).

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

Related conversions

See all energy units.