Wavelength to Frequency Calculator

Convert between the wavelength and frequency of an electromagnetic wave in a single step. Enter a wavelength (in nm, µm, mm, cm or m) to get its frequency, or enter a frequency (in Hz, kHz, MHz, GHz or THz) to get its wavelength. Alongside the conversion, the calculator reports the photon energy, the electromagnetic-spectrum band, and — for visible light — an approximate on-screen colour.

How it works

For a wave travelling through a vacuum, wavelength (λ) and frequency (f) are tied together by the speed of light:

c = λ · f

So frequency is f = c / λ and wavelength is λ = c / f. The calculator uses the exact SI value of the speed of light, c = 299,792,458 m/s.

The energy carried by a single photon of that wave follows the Planck relation:

E = h · f

using the Planck constant h = 6.626070150e-34 J·s. The result is shown in electron-volts (with 1 eV = 1.602176634e-19 J) and in joules, so you can tell at a glance whether the radiation is ionizing — photon energies above roughly 10 eV can strip electrons from atoms.

All three constants are the exact, defined values from the 2019 SI redefinition, so results are reproducible and precise.

Electromagnetic spectrum bands

Every result is classified into one of the standard spectrum bands based on its wavelength:

Band	Wavelength range	Typical sources
Gamma	< 0.01 nm	Nuclear decay, cosmic sources
X-Ray	0.01 – 10 nm	Medical imaging, high-energy astronomy
Ultraviolet	10 – 380 nm	Sunlight, sterilization lamps
Visible	380 – 750 nm	Light you can see
Infrared	750 nm – 1 mm	Thermal imaging, remote controls
Microwave	1 mm – 1 m	Wi-Fi, mobile networks, microwave ovens
Radio	> 1 m	AM/FM broadcast, shortwave

For wavelengths inside the visible window (380–780 nm), the calculator also estimates the perceived colour and shows it as an rgb() value. The colour is an approximation based on Dan Bruton's spectral-colour algorithm; the exact shade you see depends on your display's calibration.

Examples

• Green light, 550 nm converts to about 545.1 THz, with a photon energy of 2.254 eV — squarely in the visible band.
• FM radio at 100 MHz has a wavelength of about 2.998 m (radio band) and a photon energy of roughly 4.136e-7 eV.
• Wi-Fi at 2.4 GHz sits in the microwave band with a wavelength near 12.5 cm.

Does this account for the medium?

No — the conversion assumes propagation in a vacuum (which is a very close approximation for air). In a medium with refractive index n, the wave slows to v = c / n, which shortens the wavelength for the same frequency. This tool always uses the vacuum speed of light.

Everything runs entirely in your browser — nothing you type is uploaded.