Electronvolts to Joules Converter
Common Conversions
| eV | J |
|---|---|
| 0.001 | 1.602e-22 |
| 0.01 | 1.602e-21 |
| 0.026 | 4.142e-21 |
| 0.1 | 1.602e-20 |
| 1 | 1.602e-19 |
| 2 | 3.204e-19 |
| 5 | 8.011e-19 |
| 10 | 1.602e-18 |
| 13.6 | 2.179e-18 |
| 100 | 1.602e-17 |
| 1000 | 1.602e-16 |
Why this conversion matters in chemistry
The electronvolt is what atomic and molecular energies are naturally sized in. Ionization energies run a few eV to a few tens of eV, bond energies a few eV per bond, visible photons roughly 1.8 to 3.1 eV. That's a convenient range of numbers, which is exactly why spectroscopy uses it. But any calculation that ties back to thermodynamics needs joules, so you multiply by 1.602 × 10⁻¹⁹. That factor is the elementary charge — 1 eV is by definition the energy one electron picks up falling through a 1 V potential, so the conversion factor is just e in coulombs. Hydrogen's ionization energy of 13.6 eV works out to 2.18 × 10⁻¹⁸ J, which on its own is a number that tells you nothing; in eV it's one of the most memorable figures in all of physical chemistry.
Formula
Where the factor comes from
Work done moving charge through a potential difference is W = qV, and a coulomb times a volt is a joule by construction. Set q to one elementary charge and V to one volt and the electronvolt is defined: whatever e happens to be in coulombs is what 1 eV is in joules. That used to make the factor a measured quantity, tracking the best experimental value of e and inheriting its uncertainty. The 2019 SI revision ended that by fixing e at exactly 1.602176634 × 10⁻¹⁹ C, so 1 eV = 1.602176634 × 10⁻¹⁹ J is now exact by definition and will not be revised again. The electronvolt itself stays outside SI — accepted for use alongside it rather than part of it — but the bridge to the joule no longer carries an uncertainty.
Precision and significant figures
The factor is exact, so it contributes nothing and the input governs everything. That input is usually the weak link. Photoelectron binding energies read to something like 0.05 eV on a routine instrument, and an optical gap pulled off a Tauc plot is arguably no better, yet often gets written to three decimals it cannot support. Atomic ionization energies from spectroscopic term analysis are the exception, good to six or seven figures. Carry the full ten figures only inside a longer calculation chain; when the answer is written down, 1.602 × 10⁻¹⁹ covers almost every eV number a chemist meets, since four figures in gives four figures out.
Worked Examples
The ionization energy of hydrogen. The Rydberg — arguably the most iconic number in all of atomic chemistry.
The defining conversion. An electron falling through a 1 V potential picks up exactly this much kinetic energy.
The band gap of gallium nitride — a wide-bandgap semiconductor used for UV and near-UV emitters. A number worth knowing once optoelectronics enters a conversation.
Thermal energy at room temperature (kT at 298 K). The rough floor below which any barrier becomes invisible to the molecules.
Common mistakes
One particle, not one mole
13.6 eV is the ionization energy of a single hydrogen atom, and 2.179 × 10⁻¹⁸ J is that same single-atom energy wearing SI units. Reaction thermochemistry runs per mole, so setting this against a tabulated 1312 kJ/mol entry needs Avogadro's number in between. The two differ by 10²³, far enough apart that the slip announces itself — provided anyone looks at the exponent.
eV/c² and eV/c are not energies
Particle and nuclear sources write masses as eV/c² and momenta as eV/c. Both read as electronvolts at a glance and neither is one. Applying the factor to a mass quoted in eV/c² gives its energy equivalent in joules, not the mass; reaching kilograms takes a further division by c², about 8.988 × 10¹⁶. Read the slash before the value goes near the multiplier.
meV and MeV differ by a keystroke
Case is the only thing separating milli from mega on this unit, and both turn up in chemistry-adjacent work — vibrational quanta and hopping barriers in meV, core-level and nuclear transitions in MeV. A billionfold error follows from one shift key. Expanding to plain eV before the factor is applied costs nothing and puts the magnitude where it can still be questioned.