Frequency and wavelength calculator
Every wave — radio, light, sound — has a frequency and a wavelength, and the two are tied together by how fast the wave travels. This calculator converts between them: enter a frequency to get the wavelength, or a wavelength to get the frequency. It is handy for antenna sizing, optics, acoustics, and physics study.
How it works
Frequency (f), wavelength (λ) and wave speed (v) obey one relationship:
v = f × λ, so λ = v / f and f = v / λ
Choose what to solve for and the tool rearranges the formula accordingly. The default wave speed is the exact speed of light, 299,792,458 m/s, correct for radio waves and light in a vacuum. For sound in air at room temperature, change it to about 343 m/s. Frequency is entered in MHz and wavelength in metres.
Worked examples
For a 100 MHz FM signal travelling at the speed of light:
λ = 299,792,458 ÷ 100,000,000 ≈ 3 metres. A half-wave dipole antenna for FM would be about 1.5 metres long.
A 2.4 GHz Wi-Fi signal: λ = 299,792,458 ÷ 2,400,000,000 ≈ 0.125 metres (12.5 cm). Quarter-wave elements in 2.4 GHz antennas are consequently about 3 cm.
For middle C (261.63 Hz) in air at 343 m/s: λ = 343 ÷ 261.63 ≈ 1.31 metres. This tells a room-acoustic engineer how much space the fundamental needs to develop properly.
Common wave speeds
| Medium | Wave type | Speed |
|---|---|---|
| Vacuum | Light / radio | 299,792,458 m/s |
| Air at 20 °C | Sound | ~343 m/s |
| Water at 25 °C | Sound | ~1,497 m/s |
| Steel | Sound (longitudinal) | ~5,000 m/s |
| Glass (borosilicate) | Light | ~197,000,000 m/s |
For light in a medium, the speed is c divided by the material’s refractive index (n). Glass with n = 1.52 slows light to roughly 197,000 km/s, which is why wavelength shortens inside glass while frequency stays constant.
Why this relationship matters
Antenna design. Antennas are most efficient when their physical length matches a simple fraction of the wavelength (typically a half or quarter wave). Knowing the wavelength for your frequency tells you the antenna dimensions directly.
Optical filters. In optics, a 550 nm visible-green wavelength at the speed of light in vacuum corresponds to about 545 THz. Filter specifications move between frequency and wavelength depending on the manufacturer’s convention.
Acoustics. At audio frequencies, wavelengths in air are large — 17 metres at 20 Hz, 17 mm at 20,000 Hz. Room dimensions, speaker spacing, and absorption treatment are all designed around these wavelengths.
Spectroscopy. Scientists switch between wavelength (nm) and frequency (THz or wavenumber cm⁻¹) depending on the technique. This calculator converts between the two for any wave speed you specify.
Every calculation runs locally in your browser — no network requests.