Electron-Volt to Joule Converter: Energy Units

The electron-volt (eV) is a unit of energy commonly used in physics, particularly atomic, nuclear, and particle physics. One electron-volt is the energy gained by a single electron accelerated through a potential difference of 1 volt. While joules are the SI unit, electron-volts are more intuitive at subatomic scales where energy quantities are incredibly tiny.

The Formula

1 eV = 1.602 × 10⁻¹⁹ joules

To convert:

Energy (J) = Energy (eV) × 1.602 × 10⁻¹⁹
Energy (eV) = Energy (J) / 1.602 × 10⁻¹⁹

Or using the notation 1 eV = 1.602e-19 J.

Worked Example

An electron is accelerated through a 100-volt potential. What energy does it gain in joules?

Energy = 100 eV × 1.602 × 10⁻¹⁹ J/eV
       = 1.602 × 10⁻¹⁷ J

In joules, this is an incredibly small number. In eV, it's simply 100 eV — much more convenient.

Common Energy Scales in Physics

Using eV makes these scales immediately comparable.

Photon Energy

Photons have energy related to frequency:

E = h × f

Where h = 6.626 × 10⁻³⁴ J·s is Planck's constant. In eV, this becomes:

E = 4.136 × 10⁻¹⁵ eV·s × f

A photon of visible light (frequency 5 × 10¹⁴ Hz) has energy:

E = 4.136 × 10⁻¹⁵ × 5 × 10¹⁴ = 2.07 eV

Much easier than computing in joules.

Kinetic Energy in eV

In particle physics, the kinetic energy of a particle accelerated through a potential V is simply:

KE (eV) = (charge in electrons) × V (volts)

A proton accelerated through 1 million volts gains 1 million eV or 1 MeV of kinetic energy. This simplicity is why eV is standard in high-energy physics.

Tips

When working in physics, use eV for atomic scales, joules for macroscopic systems. Common multiples: keV (10³ eV), MeV (10⁶ eV), GeV (10⁹ eV), TeV (10¹² eV). Also remember that eV measures energy regardless of whether it's kinetic, electrical, or electromagnetic.

Use our Electron-Volt to Joule Converter to convert between eV and joules instantly.