Wavelength Calculator
From a single frequency, get the wavelength that one wave cycle spans and the period it takes — the two numbers behind every radio, antenna, and beam of light.
One input, two answers
Enter the frequency and the calculator returns the wavelength (c ÷ f) and the period (1 ÷ f) at once.
Use SI units
Enter the frequency in hertz (Hz) — then the wavelength comes back in metres (m) and the period in seconds (s).
What is wavelength?
Frequency in, wavelength and period out
Wavelength is the distance one full cycle of a wave spans — crest to crest. For an electromagnetic wave it is fixed by a single quantity, the frequency, because every electromagnetic wave travels at the same speed: the speed of light, c = 299,792,458 m/s in a vacuum. The relationship is wavelength = c ÷ f. Once you know the frequency, the wavelength is set — and so is the period, the time one cycle takes, period = 1 ÷ f. That makes frequency the one input you need for sizing antennas, designing radios, and working in optics or telecommunications.
Enter the frequency in hertz to get the wavelength and period instantly.
Two short formulas, both built from the frequency (f) and the fixed speed of light (c).
wavelength = c ÷ fThe wavelength is the speed of light divided by the frequency (c ÷ f). The period — the time one cycle takes — is just the reciprocal of the frequency (1 ÷ f), independent of the speed of light. Because c is constant, frequency and wavelength always move in opposite directions: a higher frequency means a shorter wavelength.
Suppose an FM radio station broadcasts at 100 MHz, that is f = 100,000,000 Hz.
Wavelength
299,792,458 ÷ 100,000,000 = 2.997925 m — about 3 metres per cycle.
Period
1 ÷ 100,000,000 = 0.00000001 s — 10 nanoseconds for one cycle.
Cross-check
Multiply back: 2.997925 × 100,000,000 ≈ 299,792,458 m/s — the speed of light.
The two outputs answer two different practical questions. The wavelength (about 3 m for a 100 MHz signal) is the physical length of one cycle in space — it tells you how big an antenna needs to be, since antennas are sized as fractions of the wavelength, and how the wave will diffract around obstacles. The period (10 nanoseconds here) is how long one cycle lasts in time — useful for timing and signal-processing work. The key insight is the inverse relationship: frequency and wavelength always multiply to the same constant speed of light, so as one rises the other falls. FM radio near 100 MHz spans about 3 m; Wi-Fi at 2.4 GHz shrinks to roughly 12.5 cm; and visible light, at hundreds of terahertz, has a wavelength of only a few hundred nanometres — which is exactly why we perceive different frequencies of light as different colours. That single trade-off explains why low-frequency radio needs large antennas while light-wave optics works at the scale of microscopes.
The formula is exact for electromagnetic waves in a vacuum, but a couple of practical points are worth keeping in mind.
Electromagnetic waves and the medium
This tool uses the speed of light, so it applies to electromagnetic waves — radio, microwaves, infrared, visible light. For sound waves you would use the speed of sound instead (about 343 m/s in air), not the speed of light. The speed of light also drops slightly in glass, water, or fibre, so the wavelength in a medium is a little shorter than the vacuum value this calculator returns. Keep the frequency in hertz so the wavelength comes back in metres and the period in seconds.