Photon Energy Calculator
Calculate the energy and frequency of a photon from its wavelength using E = hc/λ — for light, spectroscopy and quantum problems.
How it works
E = h·c ÷ λ · frequency ν = c ÷ λ · h = 6.626 × 10⁻³⁴ J·s · c = 2.998 × 10⁸ m/s
A photon’s energy is inversely proportional to its wavelength: shorter wavelengths (blue, ultraviolet) carry more energy than longer ones (red, infrared). The Planck relation E = hc/λ ties the wave picture (wavelength, frequency) to the particle picture (energy quanta). Dividing by the electronvolt gives the energy in eV, and multiplying by Avogadro’s number gives the energy of a whole mole of photons — an einstein.
Worked example
For green light at 500 nm (5 × 10⁻⁷ m): E = (6.626 × 10⁻³⁴ × 2.998 × 10⁸) ÷ (5 × 10⁻⁷) = 3.973 × 10⁻¹⁹ J, which is about 2.48 eV, or 239 kJ per mole of photons.
Sources: Photon energy — Wikipedia
Frequently asked questions
Why do shorter wavelengths have more energy?
Because energy is proportional to frequency (E = hν) and frequency is inversely proportional to wavelength (ν = c/λ). Halving the wavelength doubles both the frequency and the photon energy.
What units should the wavelength be in?
Enter it in nanometres — the usual unit for visible light (about 400–700 nm) and near UV/IR. The tool converts to metres internally before applying E = hc/λ.
What is the energy per mole of photons?
Multiplying a single photon’s energy by Avogadro’s number gives the energy of one mole of photons (an einstein), expressed here in kJ/mol so it can be compared with bond energies.
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This calculator is for educational purposes. Double-check important results before acting on them.