Wavelength & Frequency Calculator
Convert wavelength ↔ frequency, get the photon energy and the spectrum band.
Results update as you type.
About this calculator
Every wave obeys the same simple relationship: its speed equals its wavelength times its frequency, so wavelength λ = c / f and frequency f = c / λ. For electromagnetic waves in a vacuum the speed is the speed of light, c = 299,792,458 m/s (about 3 × 10⁸ m/s). Because that product is fixed, wavelength and frequency are inversely related — higher frequency always means shorter wavelength. This calculator converts either way, reports the period (T = 1 / f) and the photon energy, and names the electromagnetic band the result falls in, from radio through microwave, infrared, visible light, ultraviolet, X-ray and gamma ray.
As a worked example, an FM radio station at 100 MHz (10⁸ Hz) has a wavelength of λ = 3 × 10⁸ / 10⁸ = 3 metres — which is why FM antennas are on the order of a metre long. Green light at about 5.5 × 10¹⁴ Hz has a wavelength near 545 nm, squarely in the visible band. The tool also returns each photon’s energy from E = h × f, using Planck’s constant h = 6.62607015 × 10⁻³⁴ J·s, and shows it in both joules and electron-volts.
Higher-frequency light carries more energy per photon, which is why blue and ultraviolet light can drive chemical reactions and damage skin while radio waves cannot. You can also override the wave speed under advanced options to model waves in other media — light in glass, or sound in air — where the propagation speed differs from that of light in a vacuum. These conversions are fundamental to radio and antenna design, optics, spectroscopy and understanding the electromagnetic spectrum.
Frequently asked questions
How are wavelength and frequency related?
They are inversely related through the wave speed: λ = c / f. A higher frequency means a shorter wavelength, since their product is the constant speed of light.
How is photon energy calculated?
A photon’s energy is E = h × f, where h = 6.62607015 × 10⁻³⁴ J·s. Higher-frequency light (blue, UV) carries more energy per photon than lower-frequency light.
What are the electromagnetic spectrum bands?
In order of rising frequency: radio (below ~3 GHz), microwave, infrared, visible light (~430–770 THz), ultraviolet, X-ray and gamma ray. The calculator labels which band your frequency falls into.
Can I use it for sound or waves in other media?
Yes. Set the advanced wave-speed field to the speed in your medium — about 343 m/s for sound in air, or roughly 2 × 10⁸ m/s for light in glass — and the wavelength ↔ frequency conversion uses that speed instead of the vacuum speed of light.
What is the period of a wave?
The period is the time for one full cycle, T = 1 / f. A 100 MHz wave has a period of 10⁻⁸ s (10 nanoseconds). The tool reports the period alongside the frequency.
How do I convert a wavelength in nanometres?
Just enter it — the calculator formats results across pm, nm, µm, mm, m and km automatically. Visible light runs roughly 400 nm (violet) to 700 nm (red), so a 545 nm input lands in the green part of the visible band.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/wavelength-frequency/curl
curl "https://calculator.free/api/v1/wavelength-frequency/?solve=wavelength&frequency=100000000&wavelength=3"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/wavelength-frequency/?" + new URLSearchParams({
"solve": "wavelength",
"frequency": "100000000",
"wavelength": "3"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.