Wavelength to Energy Calculator
E = h × c ÷ λ • Photon energy in J, eV, and kJ/mol
Choose a preset medium or switch to custom speed.
Quick summary
Enter wavelength, then click Calculate.
Custom wave speed must be greater than 0.
Wavelength must be greater than 0.
h = 6.62607015×10⁻³⁴ J·s • e = 1.602176634×10⁻¹⁹ J/eV • NA = 6.02214076×10²³ mol⁻¹
Results
Energy per photon
— J
Energy per photon
— eV
Energy per mole
— kJ/mol
Wavelength
— m
Wave speed
— m/s
Results are calculated in SI units first, then shown in common energy formats.
Use this Wavelength to Energy Calculator to calculate photon energy from wavelength. Results can be shown in joules per photon, electronvolts, and kilojoules per mole.
Calculation Method
Photon energy is:
E = h × c ÷ λ
Where:
- E = photon energy
- h = 6.62607015 × 10−34 J·s
- c = wave speed
- λ = wavelength
Photon energy can also be expressed as:
E = h × f
Example
For 500 nm light in vacuum:
λ = 5 × 10−7 m
E ≈ 3.97 × 10−19 J per photon
This is approximately:
2.48 eV per photon
or
239.3 kJ/mol
Important Note
For a vacuum wavelength, use the vacuum speed of light. If wavelength is measured inside another medium, the wave speed used should correspond to that same medium. Photon energy fundamentally depends on frequency through E = hf.