Energy to Wavelength Calculator — Photon λ = hc/E
Given a photon energy in electronvolts (eV), milli-eV, kilo-eV or Joules, this calculator finds the corresponding wavelength in nanometres and metres, the frequency in Hz, and identifies the spectral region (visible, UV, X-ray, IR, etc.) using the Planck relation λ = hc/E.
Energy unit
Wavelength in nanometres (λ = hc / E)
- 1
Energy in electronvolts
E = 2 eV = 2 eVInput already in electronvolts. - 2
Wavelength (λ = hc ÷ E)
1,239.842 eV·nm ÷ 2 eV = 619.9210hc ≈ 1239.84 eV·nm — a convenient product for photon wavelength in nanometres.
How does this calculator work?
A photon's wavelength and energy are linked by λ = hc/E (hc ≈ 1239.84 eV·nm). Enter the energy in eV, meV, keV or J to get the wavelength in nm and metres, frequency in Hz, and which part of the electromagnetic spectrum it falls in — from gamma rays through visible light to radio waves.
Formula
How this is calculated
Electromagnetic radiation travels as photons, each carrying energy E = hf = hc/λ, where h is the Planck constant (6.626 × 10⁻³⁴ J·s), c is the speed of light (2.998 × 10⁸ m/s), f is frequency (Hz) and λ is wavelength (m). Rearranging for wavelength: λ = hc/E. The product hc ≈ 1239.84 eV·nm, so in convenient units λ (nm) ≈ 1239.84 / E (eV). The calculator accepts input in eV (photon physics), meV (terahertz / far-IR), keV (X-ray), or Joules.
Frequency is then f = c/λ. The spectral region is determined by the wavelength: gamma rays (<0.001 nm), X-rays (0.001–10 nm), UV (10–400 nm), visible (400–700 nm), near-IR (700–1000 nm), IR (1000 nm–0.1 mm), microwave (0.1 mm–1 m), and radio (>1 m).
This calculation applies to photons in vacuum. In a medium with refractive index n, the wavelength shortens to λ/n, but the energy and frequency are unchanged.
Frequently asked questions
Visible light spans roughly 400–700 nm, corresponding to photon energies of 1.77–3.10 eV (or 2.84–4.96 × 10⁻¹⁹ J). A green photon at 550 nm has energy ≈ 2.25 eV. Energy decreases as wavelength increases (red is lower energy than violet).
The product hc ≈ 1239.84 eV·nm lets you convert instantly without tracking powers of 10: λ (nm) = 1239.84 / E (eV). For a 2 eV photon, λ ≈ 620 nm (red). This shortcut works in the optical and near-UV/IR range where nm and eV are natural units.
Yes. When light enters a medium with refractive index n > 1 (e.g. glass with n ≈ 1.5), the wavelength shortens to λ/n while the frequency and energy remain constant. This calculator gives the vacuum wavelength, which is the standard reference value.
TG we-Calculate Editorial Team. (2026). Energy to Wavelength Calculator — Photon λ = hc/E [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/energy-to-wavelength-calculator
TG we-Calculate Editorial Team. "Energy to Wavelength Calculator — Photon λ = hc/E." TG we-Calculate. 2026. https://we-calculate.com/calculator/energy-to-wavelength-calculator.
TG we-Calculate Editorial Team, "Energy to Wavelength Calculator — Photon λ = hc/E," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/energy-to-wavelength-calculator
@misc{wecalculate_energy_to_wavelength_calculator, title = {Energy to Wavelength Calculator — Photon λ = hc/E}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/energy-to-wavelength-calculator}}, year = {2026}, note = {TG we-Calculate} }
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