How to use the electron volts to joules converter
- Enter the energy value in electron volts into the input field.
- The converter multiplies your value by
1.602176634 × 10-19automatically. - Read the result in joules displayed below the input.
How the conversion works
The electron volt is defined as the amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt. Since 2019, the elementary charge e is fixed at exactly 1.602176634 x 10-19 coulombs, making the conversion factor exact.
The formula to convert electron volts to joules is:
E(J) = E(eV) × 1.602176634 × 10-19
For example, the ionization energy of hydrogen is 13.6 eV. Multiplying gives: 13.6 × 1.602176634 × 10-19 = 2.17896022224 × 10-18 J.
Common energy values reference table
This table lists frequently encountered energies in both units for quick comparison.
| Phenomenon | Energy (eV) | Energy (J) |
|---|---|---|
| Thermal energy at 300 K | 0.02585 | 4.1416 x 10-21 |
| Red photon (700 nm) | 1.77 | 2.8359 x 10-19 |
| Green photon (532 nm) | 2.33 | 3.7331 x 10-19 |
| Hydrogen ionization | 13.6 | 2.1790 x 10-18 |
| X-ray photon (1 Angstrom) | 12,398 | 1.9864 x 10-15 |
| 1 MeV (nuclear scale) | 1,000,000 | 1.6022 x 10-13 |
Why physicists use electron volts instead of joules
The joule is the SI unit of energy, but it is impractically large for atomic and subatomic processes. A single visible-light photon carries roughly 10-19 joules, meaning calculations quickly accumulate unwieldy exponents.
The electron volt provides a human-readable scale where typical atomic transitions fall between 1 and 20 eV, nuclear reactions in the keV to MeV range, and particle accelerator collisions in GeV or TeV. Converting back to joules is only necessary when interfacing with macroscopic thermodynamic formulas or SI-based engineering standards.
Prefixes and multiples
In practice you will rarely see bare electron volts outside atomic physics. Common prefixes include:
- meV (milli-electron volt, 10-3 eV): used for phonon energies and superconducting gaps.
- keV (kilo-electron volt, 103 eV): characteristic X-rays and inner-shell binding energies.
- MeV (mega-electron volt, 106 eV): nuclear binding energies and beta decay spectra.
- GeV (giga-electron volt, 109 eV): proton rest mass is about 0.938 GeV.
- TeV (tera-electron volt, 1012 eV): Large Hadron Collider collision energies.
To convert any prefixed value to joules, first express it in plain eV, then multiply by 1.602176634 x 10-19.
Exactness of the conversion factor
Before the 2019 redefinition of SI base units, the electron volt carried experimental uncertainty because the elementary charge was measured rather than defined. Now that e is exactly 1.602176634 x 10-19 C, the relationship between electron volts and joules is mathematically exact with zero uncertainty.
This means the conversion factor has precisely nine significant digits after the decimal point in the mantissa. When converting electron volts to joules for high-precision work, you can treat the multiplier as an integer ratio rather than an approximation.
Worked examples
Each result below was produced by the same code the tool runs, so you can check your own numbers against them.
| Example | Input | Result |
|---|---|---|
| Hydrogen ionization energy | Energy in electron volts (eV): 13.6 | Joules (J): 2.17896022224 x 10^-18 |
| Visible light photon (green) | Energy in electron volts (eV): 2.33 | Joules (J): 3.73307155722 x 10^-19 |
| Thermal energy at room temperature | Energy in electron volts (eV): 0.02585 | Joules (J): 4.14162659889 x 10^-21 |
| One mega-electron volt | Energy in electron volts (eV): 1000000 | Joules (J): 1.602176634 x 10^-13 |
FAQ
How many joules are in one electron volt?
Exactly 1.602176634 x 10^-19 joules. This value is fixed by the 2019 SI redefinition of the elementary charge.
Can I convert negative electron volts to joules?
Yes. Negative eV values represent bound states or energy deficits. The conversion simply preserves the sign: multiply the negative eV value by 1.602176634 x 10^-19.
What is the difference between eV and V?
A volt (V) measures electric potential difference, while an electron volt (eV) measures energy. One eV is the energy an electron gains moving through one volt of potential.
How do I convert MeV to joules?
Multiply the MeV value by 10^6 to get eV, then multiply by 1.602176634 x 10^-19. Equivalently, multiply directly by 1.602176634 x 10^-13.
Is this conversion approximate or exact?
It is exact. Since 2019 the elementary charge is a defined constant, so the electron volts to joules conversion factor has no measurement uncertainty.
Why not just use joules for everything?
Joules are too large for atomic-scale work. Writing out 10^-19 repeatedly introduces errors and reduces readability. Electron volts keep numbers in a convenient range for quantum mechanics and particle physics.