Dipole calculator

Half-wave dipole length estimate

Uses the classic 150 / f(MHz) rule of thumb with an adjustable wire shortening factor (K). Results update instantly with monospaced figures for clarity.

Target frequency (MHz)

Wire shortening factor K

Formula:

The default shortening factor K = 0.95 suits common copper wire. Adjust for different materials or installation heights.

A half-wave dipole is one of the simplest and most widely used antennas. It consists of a single wire, cut in the middle, with a total length equal to half the wavelength (λ/2) of the target frequency. Check the for a quick conversion.

The center of the dipole has an ideal impedance of 72Ω, but this can drop to 50Ω near the ground. To connect it to your 50Ω coax, you should use a . This prevents the feedline from radiating and becoming part of the antenna.

After building, use an to check the match. If the SWR is lowest at a frequency *below* your target, the antenna is too long (trim both ends equally). If it's *above* your target, it's too short. Finally, always check your station's safety distance.