About the Volts to eV Calculator
When a charged particle moves through a voltage it gains energy, and in electronvolts that energy is simply the voltage multiplied by the charge in elementary charges. This calculator does that sum and shows the result in eV, keV and joules. Use it for an electron gun, a cathode ray tube, an ion source or a physics question about particles accelerated across a potential difference. Type the voltage and the charge and read the energy at once.
Updated October 2026
How to use the Volts to eV Calculator
- 1Enter the voltage the particle moves through.
- 2Enter its charge in elementary charges (1 for an electron or proton).
- 3Read the energy in electronvolts.
- 4Use the keV and joules rows when you need other units.
- 5Copy the result if you need it.
Energy from a potential difference
A potential difference of one volt gives one joule of energy to every coulomb that crosses it. A single electron carries 1.602176634 × 10⁻¹⁹ C, so it gains exactly 1 eV per volt. Particles with two charges gain twice as much energy from the same voltage.
Typical voltages and energies
These rough figures help you check whether an answer is sensible.
- Old TV picture tube: about 25 kV, so 25 keV electrons
- Dental X-ray tube: 60–70 kV
- Medical linear accelerator: 4–25 MV
- Van de Graaff demonstration: up to several hundred kV
Common mistakes
Forgetting the charge of the ion is the most frequent slip: a 3+ ion gains three times the energy of an electron. Another is mixing keV and eV; this calculator shows both so you can see the factor of 1,000 at a glance.
From energy to wavelength and speed
Once you have the energy in eV you can go further. For electrons, the de Broglie wavelength in nanometres is roughly 1.226 ÷ √(energy in eV) at low energies, which is why electron microscopes using tens of kV can see much finer detail than light microscopes. Photon energies convert to wavelength with λ(nm) ≈ 1,240 ÷ E(eV), so a 2 eV photon is red light near 620 nm. These shortcuts are approximations, but they show why the electronvolt is so convenient.
On phone and computer
The inputs are labelled and large enough for touch screens. On a computer the result sits next to the inputs. The arithmetic runs locally, so it is quick and private. Voltage and electron energy are tied by the charge of an electron. Reverse the sum with the eV to Volts Calculator, switch to joules with the Volts to Joules Calculator, and compare units with the Energy Converter.
Features
- Volts to eV, keV and joules
- Any charge, including multiply charged ions
- Exact value of the elementary charge
- Scientific notation for tiny numbers
- Copy result
- Works without an internet connection after loading
Frequently asked questions
How do I convert volts to eV?
Multiply the voltage by the charge in elementary charges: E(eV) = V × q. An electron crossing 5,000 V gains 5,000 eV, or 5 keV.
How much energy does a proton get from 1 MV?
A proton has a charge of 1e, so it gains 1,000,000 eV, which is 1 MeV or about 1.6 × 10⁻¹³ J.
Why use eV instead of joules?
Particle energies in joules are awkwardly small numbers. The eV keeps them easy to read and links directly to the voltages used in labs.
Does this give the speed of the particle?
No, it gives the kinetic energy. To find the speed you also need the particle's mass, and above a few keV for electrons you must use relativity.
What if the particle starts with some energy?
The result is the energy gained. Add any starting energy to get the total.
Is a negative voltage allowed?
Yes. A negative result means the particle loses that much energy, for example when it is slowed by a retarding field.
What is 1 keV in volts for an electron?
1 keV is 1,000 eV, so an electron needs to cross 1,000 V to gain it. For a 2+ ion the same energy takes only 500 V.