Wavelength & Antenna Length Calculator
Wavelength, half-wave and quarter-wave lengths from frequency and velocity factor.
Input
ℹ VF: 1.0 free space, ~0.95 wire antenna, ~0.66 coax. λ/4 = monopole/stub, λ/2 = dipole.
Results
Wavelength (λ)—
Half-Wave (λ/2)—
Quarter-Wave (λ/4)—
💡 Usage & Formula
λ = c / f × VF, c = 299.792458 m·MHz. A half-wave dipole ≈ λ/2; a quarter-wave whip ≈ λ/4.
When you need it: Sizing an antenna element (quarter-wave whip, half-wave dipole) or a matching stub from frequency, including the velocity/shortening factor of real conductors.
Worked example: At 433 MHz, λ = c/f = 0.693 m, so a quarter-wave whip is λ/4 ≈ 173 mm; apply a ~0.95 velocity factor for wire and it trims to about 164 mm.
Tips & gotchas:
- Always apply the velocity factor — ~0.95 for wire, ~0.66–0.85 for coax — or the element runs long.
- A monopole needs a ground plane; its size and shape shift the resonance and pattern.
- A quarter-wave element also resonates at odd harmonics (3×, 5× the frequency).
- Trim to resonance with a VNA; nearby metal and enclosure loading detune a "calculated" length.
📖 References:Wavelength (Wikipedia)