Electronvolts to joules (eV to J) converter

What is an electronvolts to joules converter?

An electronvolts to joules converter is an online tool that translates energy values expressed in electronvolts (eV) into joules (J), and vice versa. The two units describe the same physical quantity — energy — but they live at opposite ends of the scale. The joule is the SI unit used for everyday and engineering quantities, while the electronvolt is a tiny, convenient unit favoured in atomic, nuclear, and particle physics, where the joule would force you to drag around long strings of negative exponents.

Because a single electronvolt is an extraordinarily small amount of energy, the converter is most useful when you need to compare a microscopic process (the energy of a photon, the binding energy of an electron, the rest energy of a particle) against macroscopic, SI-based figures.

How it works

By definition, one electronvolt is the kinetic energy an electron gains when it is accelerated through an electric potential difference of one volt. Since energy equals charge multiplied by voltage, and the elementary charge is fixed at exactly 1.602176634 x 10⁻¹⁹ coulombs in the SI system, the electronvolt is locked to an exact value in joules:

• 1 eV = 1.602176634 x 10⁻¹⁹ J (exact, by definition since the 2019 SI redefinition)

To convert in the other direction, you divide by the same constant. One joule is a colossal amount of energy on the atomic scale, equal to roughly 6.241509074 x 10¹⁸ electronvolts. The converter also handles related energy units such as kilojoules (kJ), megajoules (MJ), and calories (cal) on the joule side, scaling the result accordingly.

Formula

To convert electronvolts to joules, multiply by the elementary charge in coulombs:

$E_{\text{J}} = E_{\text{eV}} \times 1.602176634 \times 10^{-19}$

To convert joules back to electronvolts, divide by the same constant:

$E_{\text{eV}} = \frac{E_{\text{J}}}{1.602176634 \times 10^{-19}}$

Electronvolts to joules conversion table

The table below lists common electronvolt values and their joule equivalents. Note how the joule figures stay extremely small, which is exactly why physicists reach for the electronvolt instead.

Examples

Example 1: Converting 1 electronvolt to joules

The fundamental conversion uses the constant directly. One electronvolt equals:

$1 \text{ eV} \times 1.602176634 \times 10^{-19} = 1.602176634 \times 10^{-19} \text{ J}$

Example 2: Converting 5 electronvolts to joules

A photon of visible-to-ultraviolet light might carry a few electronvolts of energy. Five electronvolts converts to:

$5 \text{ eV} \times 1.602176634 \times 10^{-19} = 8.01088317 \times 10^{-19} \text{ J}$

Example 3: Converting 1 joule to electronvolts

Going the other way reveals just how large a joule is at the atomic scale. One joule equals:

$\frac{1 \text{ J}}{1.602176634 \times 10^{-19}} \approx 6.241509074 \times 10^{18} \text{ eV}$

That is over six billion billion electronvolts packed into a single joule.

Notes

• Since the 2019 redefinition of the SI base units, the elementary charge is an exact value, so the eV-to-J conversion factor is exact rather than measured. Older references may quote a slightly different last digit.
• Physics problems often use multiples of the electronvolt: kilo (keV = 10³ eV), mega (MeV = 10⁶ eV), and giga (GeV = 10⁹ eV). Multiply the eV figure by the prefix before converting.
• The electronvolt is a unit of energy, not voltage, despite its name. Voltage and energy are only related through the charge being moved.
• Because joule equivalents of electronvolts are so small, scientific notation is the practical way to read these results.

Frequently asked questions

How many joules are in 1 electronvolt?

One electronvolt equals exactly 1.602176634 x 10⁻¹⁹ joules. This is the value of the elementary charge in coulombs, and it has been fixed by definition since the 2019 SI redefinition.

How many electronvolts are in 1 joule?

One joule is approximately 6.241509074 x 10¹⁸ electronvolts — more than six quintillion. You obtain this by dividing 1 by the conversion factor 1.602176634 x 10⁻¹⁹.

Why do physicists use electronvolts instead of joules?

In atomic, nuclear, and particle physics, the energies involved are minuscule when expressed in joules, leading to awkward exponents. The electronvolt keeps numbers in a readable range — a few eV for chemical bonds, keV for X-rays, MeV for nuclear reactions, and GeV or TeV for particle accelerators.

Is the electronvolt an SI unit?

No. The electronvolt is not an SI unit, but it is accepted for use alongside the SI because of its practical importance in physics. The joule remains the official SI unit of energy.

What does the prefix in keV, MeV, or GeV mean?

These are standard metric multiples of the electronvolt: keV is one thousand eV, MeV is one million eV, and GeV is one billion eV. To convert any of them to joules, multiply by the prefix first, then by 1.602176634 x 10⁻¹⁹.

Can this converter also handle kilojoules and calories?

Yes. The joule side of the converter supports joules, kilojoules, megajoules, and calories, so you can read your electronvolt energy in whichever of those units is most convenient.