How many electronvolts are in one joule?

One joule equals 6.24150907×10¹⁸ eV. This number is the reciprocal of the elementary charge in SI units (e = 1.602176634×10⁻¹⁹ C), which is now defined exactly by the 2019 SI revision.

Why are the eV values so large for everyday joule amounts?

The electronvolt is an extremely small unit — 1 eV ≈ 1.6×10⁻¹⁹ J. So any macroscopic energy measured in joules translates to an astronomically large number of eV. Scientific notation is essential to express these results.

What is the difference between eV, keV, MeV, and GeV?

1 keV = 1,000 eV; 1 MeV = 10⁶ eV; 1 GeV = 10⁹ eV. Atomic electrons are bound by a few eV, X-rays carry keV energies, nuclear reactions involve MeV, and particle accelerators reach GeV and beyond.

Is 1 eV = 1.602176634×10⁻¹⁹ J exact?

Yes. Since the 2019 redefinition of SI units, the elementary charge e is fixed at exactly 1.602176634×10⁻¹⁹ C, making 1 eV = 1.602176634×10⁻¹⁹ J an exact definition.

How do I enter scientific notation in the input?

Type it in standard e-notation: for 1.6×10⁻¹⁹ enter "1.6e-19". Most browsers and this tool accept that format directly.

Joules to Electronvolts Converter

Enter energy in joules to get electronvolts (eV), keV, MeV, and GeV — or enter eV to convert back to joules. Uses 1 J = 6.24150907×10¹⁸ eV.

Energy Converter

Energy in Joules (J)

Electronvolts (eV)

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Kiloelectronvolts (keV)

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Megaelectronvolts (MeV)

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Gigaelectronvolts (GeV)

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1 J = 6.24150907×10¹&sup8; eV | 1 eV = 1.602176634×10⁻¹&sup9; J

J ↔ eV Reference Table

Common energy values in joules and their electronvolt equivalents

Joules (J)	Electronvolts (eV)	Unit

1 eV = 1.602176634×10⁻¹&sup9; J (CODATA 2018, exact since 2019 SI revision)

Summary

This converter transforms joules (J) into electronvolts (eV), kiloelectronvolts (keV), megaelectronvolts (MeV), and gigaelectronvolts (GeV) using the exact CODATA value: 1 eV = 1.602176634×10⁻¹⁹ J. The tool is bidirectional — type in joules to get eV, or type in eV to get joules. Results use scientific notation because eV values for everyday joule quantities are extremely large.

How it works

Select the direction: Joules → eV or eV → Joules.
Enter any numeric value — whole numbers, decimals, or scientific notation (e.g. 1.6e-19).
Results in eV, keV, MeV, and GeV appear instantly.
Click any result field to copy it to the clipboard.
The reference table below shows common J↔eV conversions.

Use cases

Convert photon energy in joules to electronvolts for optics or spectroscopy problems.
Check particle accelerator beam energies against joule equivalents.
Convert binding energy or ionization energy between J and eV in chemistry homework.
Verify thermal energy (kT) expressed in joules against eV for solid-state physics.
Cross-reference nuclear reaction Q-values given in MeV with SI joules.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu