Free frequency to wavelength converter. Convert hertz, kilohertz, megahertz, gigahertz, and terahertz — and instantly find the matching wavelength using the speed of light or speed of sound. Includes period and full-spectrum context.
Hz • kHz • MHz • GHz • nm • m
Uses the exact defined speed of light, c = 299,792,458 m/s, so wavelength results are physically precise.
Tells you which band a frequency belongs to — radio, microwave, infrared, visible light, and beyond.
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Frequency and wavelength are two ways of describing the same wave, linked by the wave's speed. The fundamental equation is v = f × λ, where v is the wave speed, f is frequency (in hertz), and λ (lambda) is wavelength. Because the speed is fixed for a given medium, frequency and wavelength are inversely proportional: as one goes up, the other goes down. For electromagnetic waves (light, radio, Wi-Fi) in a vacuum, the speed is the speed of light, c = 299,792,458 m/s. For sound in air at 20°C, it's about 343 m/s.
To find wavelength from frequency: λ = c ÷ f. A 100 MHz FM radio signal has a wavelength of 299,792,458 ÷ 100,000,000 = about 3 meters. A 2.4 GHz Wi-Fi signal is about 12.5 cm. Green light at 540 THz is about 555 nanometers. To find frequency from wavelength: f = c ÷ λ. The period — how long one full cycle takes — is simply T = 1 ÷ f.
The electromagnetic spectrum runs from low-frequency radio waves (long wavelengths, meters to kilometers) through microwaves, infrared, the narrow band of visible light (roughly 400–700 nm), then ultraviolet, X-rays, and gamma rays (extremely high frequency, tiny wavelengths). Sound is mechanical, not electromagnetic, so it travels far slower — which is why a 343 Hz sound wave has a 1-meter wavelength, while a 343 Hz radio wave would be nearly 875 kilometers long.
AM radio: ~1 MHz (~300 m). FM radio: ~100 MHz (~3 m). Wi-Fi: 2.4 GHz (12.5 cm) & 5 GHz (6 cm). 5G mid-band: 3.5 GHz (8.6 cm). Microwave oven: 2.45 GHz.
Violet: ~400 nm (750 THz). Blue: ~470 nm. Green: ~550 nm (540 THz). Yellow: ~580 nm. Red: ~700 nm (430 THz). Just beyond: UV (<400 nm), infrared (>700 nm).
At 343 m/s: 20 Hz (deep bass) = 17 m. 343 Hz = 1 m. Middle A (440 Hz) = 78 cm. 20 kHz (top of hearing) = 1.7 cm. Sound wavelengths are millions of times longer than light at the same frequency.
Period T = 1/f. A 1 Hz wave takes 1 second per cycle. 1 kHz = 1 ms. 1 MHz = 1 µs. 1 GHz = 1 ns. A 3 GHz CPU clock ticks once every 0.33 nanoseconds.
Frequency and wavelength are two descriptions of the same wave, tied together by its propagation speed. For electromagnetic waves in vacuum that speed is the defined constant c, exactly 299,792,458 metres per second, which makes the conversion exact. The relationship is inverse: double the frequency and the wavelength halves. That single fact explains most of radio engineering — low frequencies have long wavelengths that diffract around obstacles and travel far, while high frequencies have short wavelengths that carry more data but are stopped by walls, which is why 5 GHz Wi-Fi is faster than 2.4 GHz but does not reach as far.
λ = c ÷ ff = c ÷ λc = 299,792,458 m/s (exact, in vacuum)In a medium: v = c ÷ n, where n is the refractive indexwhere:
Assumptions: Assumes propagation in vacuum. In coaxial cable or fibre the velocity factor is typically 0.6 to 0.9 of c, which shortens the physical wavelength and matters when cutting antennas or stubs.
Find the wavelength of a mid-band FM broadcast, then size a practical antenna.
Result100 MHz = 2.998 m wavelength (quarter-wave ≈ 75 cm)
The shortcut used by radio engineers is λ(metres) ≈ 300 ÷ f(MHz), accurate to 0.07% because c is very nearly 3 × 10⁸. Antenna elements are usually cut about 5% shorter than the theoretical length to allow for end effects in real conductors.