This antenna and frequency calculator converts between frequency and wavelength and estimates practical antenna lengths — quarter-wave and half-wave — for a target frequency. It is a quick reference for radio, Wi-Fi, antenna building, and any RF work where size and frequency are linked.
Frequency, wavelength and the speed of light
Wavelength equals the speed of light divided by frequency (λ = c ÷ f). Higher frequencies have shorter wavelengths, which is why a VHF antenna is large and a Wi-Fi antenna is tiny. The calculator converts either way, so you can find the wavelength for a frequency or the frequency for a measured wavelength.
Antenna dimensions are tied to wavelength: a half-wave dipole is about half a wavelength long and a quarter-wave whip about a quarter. In practice antennas are cut slightly shorter than the ideal because radio waves travel a little slower along a wire than in free space — a velocity factor of roughly 0.95 for thin wire — and the calculator applies this so the figure is buildable.
Building to length
Cutting an antenna to the right length tunes it to the band you want and keeps it efficient. The estimates here get you very close; final tuning trims the element while watching the standing-wave ratio (SWR). Use the calculated length as your starting point and trim, rather than cut, to final size.
Finding a quarter-wave antenna length for 100 MHz (FM band).
- Wavelength λ = 300,000,000 ÷ 100,000,000 = 3 m.
- Quarter wave = 3 ÷ 4 = 0.75 m.
- Apply ~0.95 velocity factor: 0.75 × 0.95 ≈ 0.71 m.
A quarter-wave element for 100 MHz is about 0.71 m once the velocity factor is applied.
