Photon Energy Calculator
Enter a wavelength to get the energy of a single photon in electronvolts and joules — and see why shorter wavelengths pack more punch.
Electronvolts and joules at once
Enter the wavelength and the calculator returns the photon energy in electronvolts (eV) and joules (J) together.
Use metres
Wavelength must be in metres — 500 nm is 0.0000005 m. Divide nanometres by one billion to get metres before you start.
What the photon energy calculator does
The energy of a single light particle
This photon energy calculator turns a wavelength into the energy carried by one particle of light. Light comes in discrete packets called photons, and each photon carries an amount of energy fixed entirely by its wavelength: the shorter the wavelength, the more energy. The tool takes the wavelength in metres and returns the energy in electronvolts (the handy unit for atomic scales) alongside the value in joules (the SI unit). It is the number behind the colour of light, the threshold for the photoelectric effect, and why ultraviolet light damages skin while infrared light only warms it.
Enter a wavelength in metres to get the photon energy in electronvolts and joules instantly.
Photon energy is the Planck constant times the speed of light, divided by the wavelength.
E = h·c / λThe Planck constant h is 6.62607015×10⁻³⁴ J·s and the speed of light c is 299792458 m/s — both exact SI values. Because the wavelength λ sits in the denominator, energy rises as wavelength falls. Divide the joule answer by 1.602176634×10⁻¹⁹ to express it in electronvolts.
Suppose you shine 500 nm green light, a wavelength of 0.0000005 m.
Multiply h by c
6.62607015×10⁻³⁴ × 299792458 = 1.986×10⁻²⁵ J·m — the numerator h·c.
Divide by the wavelength
1.986×10⁻²⁵ ÷ 0.0000005 = 3.97×10⁻¹⁹ J — the energy in joules.
Convert to electronvolts
3.97×10⁻¹⁹ ÷ 1.602176634×10⁻¹⁹ = 2.48 eV — the photon energy.
The two outputs are the same energy in two units. The electronvolt value (2.48 eV for green light) is the practical one for atoms and materials: it tells you whether a photon can free an electron, excite a molecule, or break a chemical bond, which typically needs a few eV. The joule value (3.97×10⁻¹⁹ J) is the SI figure you would feed into a larger energy balance. The crucial insight is that energy depends inversely on wavelength: halve the wavelength and you double the energy. That is why a 400 nm violet photon (about 3.1 eV) carries more energy than a 700 nm red one (about 1.8 eV), why ultraviolet light is energetic enough to cause sunburn, and why X-rays and gamma rays — with wavelengths thousands of times shorter — are so penetrating and ionising.
The formula is exact, but a couple of practical points are worth keeping in mind.
One photon, in metres, in a vacuum
This gives the energy of a single photon, not a beam — multiply by the number of photons for the total. Enter the wavelength in metres (convert nanometres by dividing by one billion), and note the speed of light here is the vacuum value; inside glass or water the wavelength shortens, so use the in-vacuum wavelength for the photon's intrinsic energy.