G4NSJ – Half Wave Dipole Calculator

Work out the length of a half wave dipole for any frequency. Pick a band or type your own frequency in MHz. The answer comes in metres, and in feet and inches.

Dipole calculator

Amateur band Choose a band... 160 metres (1.85 MHz) 80 metres (3.7 MHz) 60 metres (5.35 MHz) 40 metres (7.1 MHz) 30 metres (10.125 MHz) 20 metres (14.175 MHz) 17 metres (18.118 MHz) 15 metres (21.225 MHz) 12 metres (24.94 MHz) 10 metres (28.5 MHz) 6 metres (51 MHz)

Frequency in MHz

Trimming allowance None 3% longer 5% longer 10% longer

How it works:

The calculator uses the simple formula from my HF dipole aerials page. The whole length in feet is 468 divided by the frequency in MHz. Each leg is half of that. It allows for the velocity factor already, so you do not need to work it out.

Treat the answer as a starting point. The real length depends on the wire, the height, and what is nearby. That is why the calculator offers a trimming allowance. Cut the wires a little long, put the aerial up, and trim an inch or so at a time from both legs until the SWR is at its lowest. Keep the two legs the same length so the aerial stays balanced.

Choose the frequency where you do most of your operating. On a wide band such as 80 metres, the SWR will rise quickly towards the band edges, so a dipole cut for the CW end will not suit the top of the phone band.

See also HF fan dipole aerials and balanced feeders.