Wavelength Calculator
Convert between wavelength and frequency.
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Electromagnetic waves obey a single simple rule: the speed of light equals wavelength times frequency. Enter either quantity and this calculator gives you the other — plus the energy of a single photon at that frequency.
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Wavelength & Frequency — The Quick Answer
Wavelength times frequency equals the speed of light: λ × f = c. Longer waves mean lower frequencies. Visible light runs from about 380 nm (violet) to 750 nm (red).
Shortcut
c = λ × f | λ = c ÷ f | f = c ÷ λ | E = h × f
Wavelength and frequency across the spectrum
| Region | Wavelength | Frequency |
|---|---|---|
| Radio | 1 m – 100 km | 3 kHz – 300 MHz |
| Microwave | 1 mm – 1 m | 300 MHz – 300 GHz |
| Infrared | 700 nm – 1 mm | 300 GHz – 430 THz |
| Visible light | 380 – 750 nm | 400 – 790 THz |
| Ultraviolet | 10 – 380 nm | 790 THz – 30 PHz |
| X-ray | 0.01 – 10 nm | 30 PHz – 30 EHz |
Frequency stays constant as light passes between media, but wavelength changes — which is why light bends (refracts) when it enters water or glass.
How It Works
The Formulas
The wave equation for light
Formula
c = λ × f λ = c / f f = c / λ E = h × f
Variables
Speed of light
299,792,458 m/s in a vacuum — a defined constant. In a material it drops by the refractive index.
Wavelength
The distance between successive wave peaks, usually measured in nanometres for light.
Frequency
How many wave cycles pass per second, in hertz. Shorter wavelength means higher frequency.
Photon energy
Energy of one photon, E = hf, where h is Planck's constant (6.626 × 10⁻³⁴ J·s).
Note: This wave equation applies to any wave — sound, water, radio. For light in a vacuum it uses c; for other waves, substitute the appropriate wave speed.
Last updated: October 6, 2026
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Frequently Asked Questions
How do I convert wavelength to frequency?
Divide the speed of light by the wavelength: f = c ÷ λ (with λ in metres). A 500 nm green light wave has a frequency of 299,792,458 ÷ 500 × 10⁻⁹ ≈ 6.0 × 10¹⁴ Hz, or 600 THz.
What is the wavelength of visible light?
Visible light spans roughly 380 nm (violet) to 750 nm (red). Green sits near the middle at about 500–550 nm, which is why human eyes are most sensitive there.
How do I calculate photon energy?
Use E = h × f, where h is Planck's constant (6.626 × 10⁻³⁴ J·s). Higher frequency means more energetic photons — which is why ultraviolet light can damage skin while radio waves can't.
Does wavelength change in water or glass?
Yes. Frequency stays the same, but because light travels slower in a medium, its wavelength shortens by the refractive index. This change in speed is what causes refraction — the bending you see in a glass of water.