Electromagnetic Spectrum Calculator
Every electromagnetic wave, from radio through visible light to gamma rays, obeys the same simple relationships. The product of wavelength and frequency is always the speed of light, and the energy carried by a single photon is proportional to its frequency. This calculator converts an entered wavelength into frequency and photon energy using the exact SI values of the speed of light and Planck's constant. It reports energy in both joules and electronvolts so the result is useful whether you are working in physics, chemistry, optics, or radio engineering.
Electromagnetic spectrum formula
c = 299,792,458 m/s (exact)
h = 6.62607015e-34 J*s (exact)
wavelength (m) = wavelength (nm) / 1,000,000,000
frequency = c / wavelength (m)
energy (J) = h * frequency
energy (eV) = energy (J) / 1.602176634e-19
The speed of light and Planck's constant are exact defined constants in the 2019 revision of the SI. The elementary charge, used to convert joules to electronvolts, is also exact at 1.602176634 times 10 to the power minus 19 coulombs.
Spectrum facts
- Visible light spans roughly 380 to 700 nanometres; green at about 550 nm is near the peak sensitivity of the human eye.
- Radio waves have the longest wavelengths and the lowest photon energies in the spectrum.
- Gamma rays have the shortest wavelengths and the highest photon energies.
- Photon energy rises as wavelength shrinks, so ultraviolet, X-ray, and gamma photons carry enough energy to ionise atoms.
- Frequency stays constant when light enters a denser medium; the wavelength shortens instead.
Electromagnetic spectrum: frequently asked questions
What is the relationship between wavelength and frequency?
For an electromagnetic wave travelling in a vacuum, wavelength times frequency equals the speed of light c. So frequency = c / wavelength, and wavelength = c / frequency. The speed of light is defined exactly as 299,792,458 metres per second by the International System of Units (SI).
How do you calculate the energy of a photon?
Photon energy equals Planck's constant h times frequency: E = h * f. Equivalently, E = h * c / wavelength. Planck's constant is defined exactly as 6.62607015 times 10 to the power minus 34 joule-seconds in the 2019 SI redefinition. This calculator also reports energy in electronvolts (eV) for convenience.
What are the regions of the electromagnetic spectrum?
From longest to shortest wavelength: radio waves, microwaves, infrared, visible light (roughly 380 to 700 nanometres), ultraviolet, X-rays, and gamma rays. The boundaries are conventions, not sharp physical limits. Visible light is the narrow band the human eye detects.
What units should I enter?
Enter wavelength in nanometres (nm) for light, or any value you choose with the understanding that the formula converts using SI base units internally. The calculator reports frequency in hertz (Hz), energy in joules (J), and energy in electronvolts (eV).
Does this work in materials other than a vacuum?
The formulas here use the vacuum speed of light. Inside a medium with refractive index n, the wave speed and wavelength are reduced by a factor of n while the frequency stays constant. For in-medium calculations, divide the resulting wavelength by n.
Official sources
- National Institute of Standards and Technology (NIST): Speed of light in vacuum.
- National Institute of Standards and Technology (NIST): Planck constant.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.