About the eV to Volts Calculator
An electronvolt is the energy one electron gains when it moves through a potential difference of one volt. That makes converting eV to volts very simple for a single electron, but particles with more charge need a smaller voltage to gain the same energy. This calculator divides the energy in electronvolts by the charge in elementary charges to give the accelerating voltage, and shows the energy in joules as well. It suits physics homework, electron microscopes, X-ray tubes and particle accelerators.
Updated October 2026
How to use the eV to Volts Calculator
- 1Enter the energy in electronvolts. For keV multiply by 1,000; for MeV by 1,000,000.
- 2Enter the charge of the particle in elementary charges.
- 3Read the voltage needed.
- 4Look at the joules row for the same energy in SI units.
- 5Copy the result for your notes.
What an electronvolt is
The electronvolt is a tiny unit of energy used in atomic, nuclear and particle physics. Visible light photons carry about 2 to 3 eV, chemical bonds a few eV, medical X-rays tens of keV and particles in large accelerators many GeV. Using eV keeps these numbers readable instead of writing powers of ten in joules.
The formula
Energy gained = charge × voltage. Written in electronvolts and elementary charges this becomes E(eV) = q(e) × V, so V = E ÷ q.
- Electron or proton: q = 1
- Alpha particle (He²⁺): q = 2
- Ion with charge n+: q = n
Examples
An electron microscope that accelerates electrons to 200 keV uses about 200,000 V. A doubly charged oxygen ion with 30 keV of energy needs 15,000 V. An electron with 13.6 eV, the energy needed to ionise hydrogen, has crossed 13.6 V.
Checking your answer
A quick sanity check: for electrons, the voltage always equals the energy in eV. If your particle has more than one charge, the voltage must be smaller than the eV figure by that factor. If the answer is larger, the charge was probably entered as a fraction by mistake. Remember that the result is the potential difference the particle crosses, not the voltage of any particular power supply, which may need to be higher to make up for losses.
Phone or computer
Type on any device; the voltage updates instantly. Very small or very large numbers are shown in scientific notation, and nothing you enter is sent to a server. Electron energy and voltage are tied together by one charge, so it helps to switch views. Go back with the Volts to eV Calculator, convert the same energy into joules with the Volts to Joules Calculator, and compare units using the Energy Converter.
Features
- eV to volts for any charge
- Energy in joules shown too
- Works with fractional and multiple charges
- Exact elementary charge value
- Copy button
- Free and private
Frequently asked questions
How do I convert eV to volts?
Divide the energy in eV by the charge in elementary charges: V = E(eV) ÷ q(e). For an electron, q = 1, so 100 eV corresponds to 100 V.
Is 1 eV equal to 1 volt?
Not exactly; they measure different things. 1 eV is an energy, 1 V is energy per charge. For a single electron, 1 eV of energy corresponds to crossing 1 V.
What voltage gives an alpha particle 10 keV?
An alpha particle has a charge of +2e, so it needs 10,000 ÷ 2 = 5,000 V.
How many joules is 1 eV?
1 eV = 1.602176634 × 10⁻¹⁹ J, an exact value since the 2019 redefinition of SI units.
Does the sign of the charge matter?
For the size of the voltage, no. A positive ion and an electron with the same charge size need the same voltage, only in opposite directions.
Can I enter keV or MeV?
Type the value in eV: 5 keV is 5,000 eV and 2 MeV is 2,000,000 eV. Our Volts to eV calculator goes the other way and also shows keV.