Antenna Length Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the frequency in MHz.
- Optionally set the velocity factor (about 0.95 for real wire; 1.0 for the theoretical wavelength).
- Read the full, half and quarter-wave lengths.
How it works
The Antenna Length Calculator finds antenna element lengths from the operating frequency. A quarter-wave is the usual length for a vertical or whip antenna, and a half-wave for a dipole.
Wavelength λ = 300 ÷ frequency in MHz (metres). The physical element is shorter than the free-space wavelength, so it's multiplied by a velocity factor (roughly 0.95 for wire). The lengths shown are λ, λ/2 and λ/4 after that adjustment.
Worked example
2 m band, 146 MHz. λ ≈ 2.05 m; with a 0.95 velocity factor a quarter-wave whip is about 0.49 m.
Frequently asked questions
What is the velocity factor?
Radio waves travel a little slower along a wire than in free space, so the resonant element is slightly shorter than the theoretical wavelength. A factor of about 0.95 is typical for bare wire.
Quarter-wave or half-wave?
A quarter-wave is the common length for a ground-plane vertical or whip (it needs a ground/counterpoise); a half-wave is used for a dipole. Pick the length for your antenna type.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.