Wavelength to Energy Calculator — Photon Energy (E = hc/λ)
Enter a wavelength (in nanometres, micrometres, Ångströms, or metres) to instantly get the energy of a single photon in joules and electron-volts, plus frequency and wavenumber.
Unit
Energy of a single photon at this wavelength (electron-volts)
- 1
Wavelength in metres
500 × 1e-9 = 5.000e-7 m - 2
Product hc (Planck × speed of light)
6.626e-34 × 2.998e+8 = 1.986e-25 J·mA fixed physical constant — Planck's constant times the speed of light. - 3
Photon energy E = hc ÷ λ
1.986e-25 ÷ 5.000e-7 = 3.973e-19 J - 4
Energy in electron-volts
3.973e-19 ÷ 1.602e-19 = 2.4797
How does this calculator work?
Photon energy E = hc/λ, where h = 6.626×10⁻³⁴ J·s and c = 2.998×10⁸ m/s. Enter a wavelength in any unit (nm, μm, Å…) and the calculator returns energy in joules and electron-volts, frequency in Hz, and wavenumber in cm⁻¹. Visible light spans roughly 1.8–3.1 eV.
Formula
How this is calculated
A photon’s energy is inversely proportional to its wavelength: the shorter the wave, the more energy it carries. The Planck–Einstein relation E = hc / λ formalises this, where h is Planck’s constant (6.62607015 × 10⁻³⁴ J·s) and c is the speed of light in vacuum (2.99792458 × 10⁸ m/s). The product hc ≈ 1.986 × 10⁻²⁵ J·m, so a 500 nm green photon carries about 3.97 × 10⁻¹⁹ J or 2.48 eV.
Electron-volts (eV) are the preferred unit in optics and particle physics because the numbers are human-scale: visible light photons carry roughly 1.8–3.1 eV, UV photons carry 3–100 eV, and X-ray photons carry hundreds to hundreds of thousands of eV. The joule value is minuscule but is needed for thermodynamic calculations. The calculator also reports frequency (f = c/λ) and wavenumber in cm⁻¹ (1/λ when λ is in centimetres), which spectroscopists commonly use.
The formula applies only to photons in vacuum (or approximately in air). In a medium with refractive index n, the wavelength shortens to λ/n while frequency stays the same. The energy is still E = hf = hc/λ_vacuum — use the vacuum wavelength, not the in-medium value, for energy calculations.
Frequently asked questions
1 eV of photon energy corresponds to a wavelength of about 1240 nm — in the near-infrared, just outside the visible range. The relation λ (nm) ≈ 1240 / E (eV) is a handy shortcut widely used in photonics and semiconductor physics.
Energy is proportional to frequency (E = hf), and frequency is inversely proportional to wavelength (f = c/λ). So halving the wavelength doubles the frequency and doubles the photon energy. UV light is more energetic than visible light for exactly this reason.
Yes — radio, microwave, infrared, visible, UV, X-rays and gamma rays all follow E = hc/λ. The values simply span many orders of magnitude: a 1 m radio wave photon carries only ~1.24 μeV, while a 0.001 nm gamma-ray photon carries over 1 MeV.
Also known as
TG we-Calculate Editorial Team. (2026). Wavelength to Energy Calculator — Photon Energy (E = hc/λ) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/wavelength-to-energy-calculator
TG we-Calculate Editorial Team. "Wavelength to Energy Calculator — Photon Energy (E = hc/λ)." TG we-Calculate. 2026. https://we-calculate.com/calculator/wavelength-to-energy-calculator.
TG we-Calculate Editorial Team, "Wavelength to Energy Calculator — Photon Energy (E = hc/λ)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/wavelength-to-energy-calculator
@misc{wecalculate_wavelength_to_energy_calculator, title = {Wavelength to Energy Calculator — Photon Energy (E = hc/λ)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/wavelength-to-energy-calculator}}, year = {2026}, note = {TG we-Calculate} }
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