Antenna Length & Wavelength
Wavelength λ = c/f plus half-wave dipole and quarter-wave whip lengths, with velocity factor and end-effect correction.
Edit f or λ — the other follows. VF ≈ 0.95 for insulated wire; k ≈ 0.95 trims the dipole for end effects.
From frequency to antenna length
An electromagnetic wave travels at the speed of light, so its wavelength is just light speed divided by frequency. In a real conductor or coating the wave slows down by the velocity factor:
A resonant element is a fraction of that wavelength. Real metal rods radiate as if slightly longer than they are (the end effect), so we shorten the physical length by a factor :
This is why a half-wave dipole is a touch shorter than the electrical λ/2. A quick field shortcut in metres is for the full dipole, which lands within a centimetre of the exact formula across the HF and VHF bands.
Frequently asked questions
How do I calculate antenna length from frequency?
First find the wavelength λ = c / f with c = 299,792,458 m/s, then take a fraction of it. A half-wave dipole is k·λ/2 and a quarter-wave whip is k·λ/4, where k ≈ 0.95 trims for end effects. At 100 MHz, λ = 2.998 m, so the dipole is 0.95 × 2.998 / 2 ≈ 1.424 m.
What is the wavelength formula?
Wavelength equals the speed of light divided by frequency: λ = c / f, where c = 299,792,458 m/s. In a cable or coated element multiply by the velocity factor: λ = c·VF / f. For 2.4 GHz in free space, λ = 299,792,458 / 2.4e9 ≈ 0.125 m (12.5 cm).
How long is a half-wave dipole?
A half-wave dipole is about k·λ/2 with k ≈ 0.95 to account for the end effect, slightly shorter than the electrical λ/2. A handy shortcut in metres is L ≈ 143 / f(MHz). At 100 MHz that's 143 / 100 = 1.43 m, matching 0.95 × 2.998 / 2 ≈ 1.424 m.
What is velocity factor?
Velocity factor (VF) is how much slower a wave travels in a medium versus free space, from 0 to 1. It shortens the wavelength: λ = c·VF / f. Bare wire is near 1.0, insulated wire about 0.95, and coax typically 0.66–0.85, so resonant lengths shrink by that same factor.