Joules to electronvolts (J to eV) converter

What is a joules to electronvolts converter?

A joules to electronvolts converter is an online tool that translates an amount of energy expressed in joules (J) into its equivalent in electronvolts (eV), and back again. Both are units of energy, but they live at very different scales: the joule is the SI unit used for everyday and macroscopic measurements, while the electronvolt is a tiny unit favored in atomic, nuclear, and particle physics. Bridging these two units lets you compare laboratory-scale energies with the energies of individual particles without juggling awkward powers of ten by hand.

How it works

The electronvolt is defined as the kinetic energy gained by a single electron when it is accelerated through an electric potential difference of one volt. Because the elementary charge is exactly 1.602176634 × 10⁻¹⁹ coulombs, one electronvolt equals exactly 1.602176634 × 10⁻¹⁹ joules. This makes the conversion a simple multiplication or division by that constant. Since one joule contains the energy of roughly 6.24 × 10¹⁸ electrons accelerated through one volt, even a small everyday energy translates into an enormous number of electronvolts.

To use the converter, enter a value in either field. Type into the joules box to see the electronvolt equivalent, or type into the electronvolts box to get the value in joules. The unit selectors let you switch between joules, kilojoules, megajoules, calories, and electronvolts so you can work with whatever scale fits your problem.

Formula

To convert joules to electronvolts, divide by the elementary charge:

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

To convert electronvolts to joules, multiply by the same constant:

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

Joules to electronvolts conversion table

The table below shows common joule values and their electronvolt equivalents using the exact conversion factor.

Examples

Example 1: Converting 1 joule to electronvolts

Divide one joule by the elementary charge:

$\frac{1}{1.602176634 \times 10^{-19}} = 6.241509 \times 10^{18} \text{ eV}$

So 1 joule is approximately 6,241,509,074,000,000,000 electronvolts.

Example 2: Converting 1 electronvolt to joules

Multiply one electronvolt by the constant:

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

A single electronvolt is therefore an extremely small amount of energy in joules.

Example 3: Converting 2 joules to electronvolts

$\frac{2}{1.602176634 \times 10^{-19}} = 1.248302 \times 10^{19} \text{ eV}$

Two joules equal about 1.248302 × 10¹⁹ electronvolts, exactly double the value for one joule.

Notes

• The conversion factor 1.602176634 × 10⁻¹⁹ is an exact value fixed by the 2019 redefinition of SI base units, so results are limited only by the precision of your input.
• Electronvolts are most useful at microscopic scales; physicists often use multiples such as keV (10³ eV), MeV (10⁶ eV), and GeV (10⁹ eV) for higher energies.
• Energy values in joules and electronvolts describe the same physical quantity, so a result is meaningful regardless of which unit you read it in.
• Because the electronvolt is so small, even tiny joule values produce very large electronvolt numbers expressed in scientific notation.

Frequently asked questions

How many electronvolts are in 1 joule?

One joule equals approximately 6.241509 × 10¹⁸ electronvolts, which is the reciprocal of the elementary charge in coulombs.

What is the exact value of 1 electronvolt in joules?

One electronvolt is exactly 1.602176634 × 10⁻¹⁹ joules. This value comes from the elementary charge, which was fixed as an exact constant in the 2019 SI redefinition.

Why is the electronvolt used instead of the joule in physics?

The joule is far too large for atomic and subatomic energies, which would otherwise be written with cumbersome negative exponents. The electronvolt keeps these numbers in a convenient range, making it the standard unit in particle, nuclear, and atomic physics. If you need to go the other way, you can use our electronvolt to joule converter.

Can I convert kilojoules or megajoules to electronvolts here?

Yes. Use the unit selector to choose kilojoules (kJ) or megajoules (MJ) in the joules field, and the converter will scale to joules first before giving the electronvolt result. You can also explore our joule to megajoule converter.

Does converting between joules and electronvolts change the amount of energy?

No. Both are simply different units for the same physical quantity, so a conversion only changes how the number is expressed, never the underlying energy.

Why are my electronvolt results shown in scientific notation?

Because one joule equals billions of billions of electronvolts, the numbers quickly become extremely large. Scientific notation keeps these values readable while preserving their precision.