Volt to Electron Volt (eV) Calculator
Enter a voltage and a charge to convert from volts to electron volts (eV). Choose whether your charge is given in elementary charges (the number of electrons) or in coulombs. The result updates instantly, and you also get the equivalent energy in joules. Switch to reverse mode to convert eV back to volts.
What is an electron volt?
An electron volt (eV) is a unit of energy defined as the amount of kinetic energy gained by a single electron (or proton) when it accelerates through an electric potential difference of exactly one volt in a vacuum. Because the charge of one electron is 1.602176634 x 10^-19 coulombs (an exact defined value since the 2019 SI redefinition), one electron volt equals exactly 1.602176634 x 10^-19 joules. The electron volt is not an SI unit, but it is widely accepted in atomic, nuclear, and particle physics because it produces conveniently sized numbers where joules would give awkward exponents. Photon energies, chemical bond energies, ionisation energies, and particle beam energies are all routinely quoted in eV, keV, MeV, or GeV.
How to convert volts to electron volts
Volts and electron volts measure different physical quantities: volts measure electric potential (energy per unit charge), while electron volts measure energy directly. You cannot convert one to the other without specifying an amount of charge. The general formula is: E(eV) = V(V) x Q(e), where Q(e) is the charge expressed in multiples of the elementary charge. If the charge is given in coulombs instead, the formula becomes: E(eV) = V(V) x Q(C) / 1.602176634 x 10^-19. For a single electron (Q = 1 e) the formulas simplify to E(eV) = V numerically, which is the definition of the electron volt. For 40 electrons accelerated through 20 V: E = 20 x 40 = 800 eV. For a charge of 2 C through 20 V: E = 20 x 2 / 1.602176634 x 10^-19 = approximately 2.497 x 10^20 eV.
Metric prefixes for electron volts
The electron volt is used across an enormous range of energies, so metric prefixes are essential. One kiloelectron volt (keV) equals 1000 eV and is the unit of X-ray photon energies and the K-edge absorption energies of heavy elements. One megaelectron volt (MeV) equals 10^6 eV and describes nuclear reaction Q-values and the rest-mass energy of electrons (0.511 MeV). One gigaelectron volt (GeV) equals 10^9 eV and is the scale of proton rest mass (938.3 MeV) and accelerator energies. One teraelectron volt (TeV) equals 10^12 eV and is the energy frontier of the Large Hadron Collider. This calculator returns the result in plain eV; divide by 1000 for keV, by 10^6 for MeV, and so on.
Reverse conversion: electron volts to volts
To find the accelerating voltage required to give a charged particle a target kinetic energy, rearrange the formula: V(V) = E(eV) / Q(e). For a single electron (Q = 1 e) the voltage numerically equals the energy in eV, so a 10 keV X-ray tube requires a 10,000 V accelerating potential. For a multiply charged ion with charge Z (in units of e), divide the required eV by Z to get the voltage. Use the reverse mode toggle on this calculator to perform that calculation directly.
Energy scale in electron volts
| Phenomenon | Typical energy | Scale |
|---|---|---|
| Chemical bond (covalent) | 1-10 eV | eV |
| Visible light photon | 1.7-3.3 eV | eV |
| Ultraviolet photon | 3.3-100 eV | eV |
| X-ray photon (soft) | 100 eV - 10 keV | keV |
| X-ray photon (hard) | 10-100 keV | keV |
| Radioactive gamma ray | 0.1-10 MeV | MeV |
| Alpha particle (typical) | 3-9 MeV | MeV |
| Cosmic ray proton (typical) | 1-100 GeV | GeV |
| LHC proton beam (design) | 6500 GeV (6.5 TeV) | TeV |
Common phenomena and their characteristic energies in eV.
Frequently asked questions
Why do I need to enter a charge to convert volts to eV?
Because volts and electron volts measure different things. A volt is electric potential, which is energy per unit charge (J/C). An electron volt is a specific amount of energy. To get energy from a potential you must multiply by a charge: E = V x Q. Without a charge value, the conversion is undefined. The special case where the charge is exactly one elementary charge (one electron) is precisely the definition of the electron volt, which is why 1 V accelerating one electron produces exactly 1 eV.
What is the difference between elementary charge and coulombs?
The elementary charge (symbol e) is the magnitude of the electric charge carried by a single proton or electron: e = 1.602176634 x 10^-19 C exactly. When you set the charge mode to elementary charges and enter 40, that means 40 electrons. In coulombs mode, you enter the charge directly in SI units. For everyday electronics the coulomb is the natural unit; for atomic and particle physics counting individual electrons or ions is more natural.
Is the electron volt an SI unit?
No. The SI unit of energy is the joule. The electron volt is a non-SI unit that is accepted for use with the SI because it is so convenient in particle and atomic physics. The exact conversion is 1 eV = 1.602176634 x 10^-19 J, a value fixed by the 2019 redefinition of the SI which made the elementary charge an exact defined constant.
How many eV is a visible-light photon?
Visible light spans roughly 400-700 nm in wavelength, corresponding to photon energies of about 1.77-3.10 eV. Red light at 700 nm is about 1.77 eV, green at 550 nm is about 2.26 eV, and violet at 400 nm is about 3.10 eV. These energies are comparable to chemical bond energies, which is why photons of visible light can drive photochemical reactions such as photosynthesis and photography.
How do I convert keV or MeV back to volts?
Use the reverse mode on this calculator. Enter the energy in eV (multiply keV by 1000 or MeV by 1,000,000 first), set the charge to 1 elementary charge if you mean a singly charged particle, and the calculator returns the required voltage. For example, 10 keV = 10,000 eV through 1 electron requires 10,000 V, the operating voltage of a typical dental X-ray machine.