Electronvolt (eV)
eV is the electronvolt, a unit of energy: the energy an electron gains when it is accelerated through one volt. One electronvolt is exactly 1.602 176 634 × 10⁻¹⁹ joules.
How to read it
The BIPM’s SI Brochure lists the electronvolt among the non-SI units accepted for use with the SI, and says the conversion to joules has been exact since 2018, when the value of the elementary charge was fixed; NIST’s CODATA table marks it exact too. OpenStax’s University Physics explains what it is for: the energy of one electron is a tiny fraction of a joule, so a smaller unit is handier. An electron accelerated through 50 V gains 50 eV, and through 100,000 V (100 kV), 100 keV. It takes the SI prefixes, as in 80 MeV, 80 megaelectronvolts (NIST SP 811), and OpenStax gives the Planck constant in both units, 6.626 × 10⁻³⁴ J·s or 4.136 × 10⁻¹⁵ eV·s.
Also searched as: electron volt, electron-volt, electronvolt symbol, eV, eV unit, GeV, keV, MeV.
How it is written
The BIPM and NIST write electronvolt as one word; OpenStax writes electron-volt. The symbol is eV either way, with a capital V because the volt is named after a person: NIST’s rule is that a unit symbol starts with a capital letter when the unit’s name comes from a person’s name.
Read next
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- The same shape in Coin gradesFBL (full bell lines)FBL means full bell lines: on a Franklin half dollar, the horizontal lines across the bottom of the Liberty Bell on the reverse are fully struck. PCGS, NGC and CAC Grading each word the requirement a little differently.
More physics and chemistry symbols
The same shape elsewhere
Browse symbols drawn with letters and numbers.
Sources
- The International System of Units (SI), 9th edition, SI Brochure, 9th edition (2019), updated 2024, Bureau International des Poids et Mesures (BIPM), Table 8 and note (l)
- University Physics Volume 2, 7.2 Electric Potential and Potential Difference, OpenStax (Rice University), The Electron-Volt
- CODATA Value: electron volt, The NIST Reference on Constants, Units and Uncertainty (2022 CODATA), National Institute of Standards and Technology, electron volt
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Sec. 6.2.8; Sec. 6.1.2
- University Physics Volume 3, 6.1 Blackbody Radiation, OpenStax (Rice University), Equation 6.10
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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