Wavelength Calculator
Convert between frequency and wavelength with an optional velocity factor, and get the half-wave and quarter-wave lengths.
Frequency and wavelength
A wave's wavelength is the distance it travels in one cycle: the wave speed divided by its frequency. In free space electromagnetic waves travel at the speed of light, c ≈ 299 792 458 m/s.
λ = v / f, where v = c × velocity factor
The velocity factor accounts for waves travelling slower than light through a cable or antenna element — around 0.66 for common coax and 0.95–0.98 for bare antenna wire. The half-wave and quarter-wave figures are handy starting points for antenna element lengths.
How it works
Frequency and wavelength are two ways of describing the same wave, tied together by its speed: multiply them and you get the wave's velocity. Since that velocity is fixed for a given medium, the two are inversely proportional — raise the frequency and the wavelength shrinks in exact proportion. In free space the velocity is the speed of light, so a 100 MHz FM signal has a wavelength of about 3 m, while a 2.4 GHz Wi-Fi signal is only about 12.5 cm. That shrinking is why higher-frequency antennas are physically smaller.
Worked example: a quarter-wave antenna
To make a quarter-wave whip for 433 MHz, first find the wavelength: λ = 299 792 458 / 433 000 000 ≈ 0.692 m. A quarter of that is about 173 mm — but real wire runs a touch slower than light, so applying a velocity factor of ~0.95 trims it to around 164 mm. The calculator's quarter-wave output does this for you; the velocity factor is why a cut element is always slightly shorter than the free-space figure.
Where it's used
Wavelength sets antenna dimensions, the spacing of elements in an array, and the physical length of resonant stubs and transmission-line sections. For circuit resonance rather than physical wavelength, see theLC resonant frequency andreactance calculators; for radio range, the free-space path loss calculator.
Velocity factor is not a constant
Wavelength in free space is exact, but inside a cable it depends on the velocity factor, and that is a property of the specific cable rather than a universal figure. Foam dielectric runs around 0.85, solid polyethylene around 0.66, and nominally identical cable from different manufacturers can differ by a few percent. It also shifts slightly with temperature and frequency. For cutting a quarter-wave stub, use the manufacturer's figure and cut long — trimming is easy, and lengthening is not.