Find the length of a half-wave dipole for any frequency, total length and each leg, in feet and metres.
A half-wave dipole is the most common ham antenna. Total length in feet = 468 / frequency in MHz, split into two equal legs fed at the centre. The 468 figure already allows for the end effect that makes a real wire resonate a little shorter than a free-space half wavelength. Trim for lowest SWR.
Total length in feet is 468 divided by the frequency in MHz, in metres it is about 142.6 divided by MHz. For example a 20m dipole at 14.2 MHz is about 32.96 feet (10.05 m) total, with two legs of 16.48 feet each.
A free-space half wavelength would use 492, but a real wire has an end effect that makes it resonate slightly short, so the practical figure is 468. Thicker wire and insulation shift it a little, so cut a touch long and trim for lowest SWR.
Higher is generally better. At least a quarter wavelength up helps efficiency and lowers the takeoff angle for DX; lower antennas radiate more straight up, which suits regional (NVIS) contacts.