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Electronvolts (eV) to Joules Converter

Enter a value in electronvolts (ev) to convert it to joules, kj per mole.

How it is calculated

Enter an energy in electronvolts (eV). The tool multiplies it by two constants. J = eV × 1.602176634×10⁻¹⁹ gives the energy of a single particle in joules, shown in scientific notation with four decimals, such as 2.1790e-18. kJ/mol = eV × 96.485332 gives the energy of one mole of particles, using the Avogadro number, and is shown with four decimals in kJ/mol.

The first factor is the exact SI value of the elementary charge. Any number is accepted, including zero and negatives, which are simply converted with their sign. The two answers describe different things: joules is the energy for one particle or photon, while kJ/mol is the energy for 6.022×10²³ of them. Prefixed units such as keV or MeV must be converted to eV first (1 MeV is 1,000,000 eV).

Worked example

An energy of 13.6 eV, close to the energy needed to ionise a hydrogen atom from its ground state. Joules: 13.6 × 1.602176634e-19 = 2.1790e-18 J. Per mole: 13.6 × 96.485332 = 1,312.2005 kJ/mol. The same electronvolt value therefore reads as a tiny number per particle but a large one per mole.

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Common mistakes

  • Entering keV or MeV values as plain eV. 5 MeV must be typed as 5000000, otherwise the answer is a million times too small.
  • Comparing joules with kJ/mol directly. One is per particle and the other per mole, so they differ by the Avogadro number and by the 1,000 of kilo.
  • Misreading the scientific notation. 2.1790e-18 J is 0.0000000000000000021790 J, not 2.179 J.
  • Using the result for a wavelength or frequency. Converting energy to wavelength needs a further step with Planck’s constant, which this tool does not do.
  • Confusing electronvolts with volts. The volt is a unit of potential, while the electronvolt is a unit of energy.

About this calculator

The electronvolt (eV) is the energy gained by a single electron accelerating through a potential difference of one volt — a convenient scale for atomic and subatomic physics, where a joule is astronomically too large. Since the 2019 SI redefinition fixed the elementary charge exactly, the conversion is now an exact constant: 1 eV = 1.602176634 × 10⁻¹⁹ J. Scaled by Avogadro's number, an energy per particle becomes a molar energy: 1 eV per particle is about 96.485 kJ/mol, the standard chemistry energy scale.

Particle and nuclear physicists work natively in eV, keV, MeV and GeV to express particle energies, binding energies, and photon energies (via E = hc/λ); chemists convert to kJ/mol to compare against bond energies and reaction enthalpies measured on a per-mole basis.

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