🔆 Photon Energy Calculator (E = hf)
Find a photon’s energy from its frequency or wavelength (E = hf = hc/λ), shown in joules and eV.
Photon energy E
3.9729e-19 J (2.480e+0 eV)
Photon energy E = h·f = h·c/λ, with h = 6.626×10⁻³⁴ J·s, c = 3×10⁸ m/s. Result also shown in eV. 🔒 Computed in your browser.
How the photon energy calculator (e = hf) works
A photon’s energy is E = hf, where h is Planck’s constant (6.626×10⁻³⁴ J·s) and f the frequency; equivalently E = hc/λ. Enter a wavelength or frequency and the tool gives the energy in joules and electronvolts. A handy shortcut is E(eV) ≈ 1240 / λ(nm): a photon’s energy in electronvolts is roughly 1240 divided by its wavelength in nanometres.
The joule↔eV conversion is a common stumbling point; the tool shows both. Shorter wavelength (higher frequency) means a more energetic photon, why UV damages skin but radio waves don’t.
Frequently asked questions
How do I calculate photon energy?
E = hf, or E = hc/λ from the wavelength. A 500 nm photon has E = hc/λ ≈ 3.97×10⁻¹⁹ J ≈ 2.48 eV. Enter frequency or wavelength.
What is Planck’s constant?
h = 6.62607015×10⁻³⁴ J·s (an exact defined value since 2019). It sets the energy of a photon per unit frequency.
How do I convert photon energy to eV?
Divide joules by the elementary charge (1.602×10⁻¹⁹). The tool shows the electronvolt value automatically.
Why do shorter wavelengths carry more energy?
Because E = hc/λ, energy is inversely proportional to wavelength. UV and X-rays (short λ) are far more energetic than visible or radio waves.
What is a photon?
A quantum (particle) of light. Its energy depends only on frequency (or wavelength), not intensity, brighter light means more photons, not more energetic ones.
Worked example: green light
For a 550 nm photon, E ≈ 1240/550 ≈ 2.25 eV, or in joules E = hc/λ = (6.626×10⁻³⁴ × 3×10⁸)/(550×10⁻⁹) ≈ 3.6×10⁻¹⁹ J.
What is the 1240 shortcut?
Because hc ≈ 1240 eV·nm, the photon energy in electronvolts is about 1240 divided by the wavelength in nanometres, a fast way to check visible-light photon energies, which run roughly 1.6-3.3 eV.
What is the photoelectric effect?
Light ejects electrons from a metal only when each photon carries enough energy (E = hf) to overcome the metal’s work function. It depends on frequency, not brightness, key evidence that light is quantised into photons.
How many photons are in a beam of light?
Divide the total light energy by the energy per photon (E = hf). Because each visible photon carries only a few electronvolts, even a dim source emits enormous numbers of photons every second.