Photon Energy Calculator
A photon is the fundamental particle of light and all other electromagnetic radiation. Its energy is determined entirely by its frequency or, equivalently, its wavelength: higher frequency means more energy. The relationship is captured by two equivalent formulas. When you know the wavelength, use E = hc divided by lambda, where h is Planck's constant (6.626 times 10 to the power of negative 34 joule seconds) and c is the speed of light in a vacuum (2.998 times 10 to the power of 8 metres per second). When you know the frequency, use E = hf. Because photon energies at the atomic scale are tiny in joules, results are also given in electronvolts (eV), where 1 eV equals 1.602 times 10 to the power of negative 19 joules. Visible light spans roughly 380 nm (violet, about 3.26 eV) to 700 nm (red, about 1.77 eV). Ultraviolet photons carry enough energy to break chemical bonds, which is why sunscreen matters. X-ray and gamma-ray photons are more energetic still. This calculator accepts wavelength in nanometres or frequency in hertz and returns energy in both joules and electronvolts along with the corresponding frequency or wavelength. It is used in quantum mechanics, spectroscopy, photochemistry, solar cell design and radiation physics courses. Results use internationally accepted constants and are for educational and reference use.
Constants used: h = 6.626 x 10⁻³⁴ J s, c = 2.998 x 10⁸ m/s, 1 eV = 1.602 x 10⁻¹⁹ J.
How it works
From wavelength: convert lambda from nanometres to metres (multiply by 1e-9), then apply E = hc / lambda. From frequency: apply E = hf directly. Convert to electronvolts by dividing the joule value by 1.602 x 10 to the power of negative 19. To find frequency from wavelength use f = c / lambda; to find wavelength from frequency use lambda = c / f, then convert metres to nanometres.
Worked example
A photon has a wavelength of 500 nm (green visible light). Converting: 500 nm = 5.00 x 10 to the power of negative 7 m. Energy E = (6.626e-34 x 2.998e8) divided by 5.00e-7 = 1.9864e-25 divided by 5.00e-7 = 3.97 x 10 to the power of negative 19 J. In electronvolts: 3.97e-19 divided by 1.602e-19 = 2.48 eV. These match the default values pre-filled above.
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