Photon energy calculator
Enter the wavelength in nanometers to get the energy of one photon from the Planck relation. Suited to modern physics and photochemistry work.
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How to use it
- Enter wavelength.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
E = h c / λ with h = 6.62607015 × 10⁻³⁴ J·s and c = 299792458 m/s; 1 eV = 1.602176634 × 10⁻¹⁹ J.
Example
Inputs: Wavelength = 500 nm. Result: Photon energy: 2.479684 eV; Energy in joules: 3.97289e-19 J; Frequency: 599,584,916,000,000 Hz.
Limits and caveats
- Enter the vacuum wavelength. If you have the wavelength inside a medium, multiply it by that medium's refractive index first.
Questions about this tool
What is the quick rule for energy in eV?
Divide 1239.84 by the wavelength in nm, so red light at 650 nm carries about 1.91 eV.
Why does violet light carry more energy than red?
Energy is inversely proportional to wavelength, and violet has the shorter wavelength.
What is the energy per mole used for?
Chemists use it to compare light energy with bond energies, which are usually given in kJ/mol.