Antenna Length Calculator

Enter your frequency in MHz to get a starting length for a half-wave dipole or a quarter-wave vertical, in feet and metres.

Half-wave dipole, total length

10.05 m (32.96 ft)

Starting length: cut long and trim.

Each dipole leg

5.02 m / 16.48 ft

Quarter-wave

5.02 m / 16.48 ft

Wavelength (free space)

21.11 m

Frequency (MHz)Shortening factor1 = standard 468 and 234 formulas

How it works

Type the centre frequency in MHz (for example 14.2 for the 20 m amateur band).
Leave the shortening factor at 1 for the standard formulas, or change it to fit your wire.
Read the total dipole length, the length of each leg and the quarter-wave length.
Cut slightly long, then trim while checking the standing wave ratio with an antenna analyser.

Amateur radio dipoles
Get the first cut length for a wire dipole on any band.
Quarter-wave verticals
Find the radiator and radial length for a ground-plane antenna.
Comparing bands
See how the length changes from 40 m to 10 m.

What formulas are used?: Half-wave dipole: 468 ÷ frequency in MHz gives the total length in feet. Quarter-wave: 234 ÷ frequency in MHz, also in feet. Metres are the feet value × 0.3048. The 468 constant is about 5% shorter than the free-space half wavelength (492 ÷ f), which allows for end effects on typical wire.
Is this the final length?: No, it is a starting point. Height above ground, nearby objects, wire thickness and insulation move the resonant frequency, so trim and measure. The sources behind these constants are amateur-radio references and calculators, not a standards document.
What does the shortening factor do?: It multiplies the result. Leave it at 1 for the standard 468 and 234 formulas, or use a value below 1 if your own measurements show your antenna resonates lower than predicted.