This app is intended for aiding in the design of simple wire dipole antennas for 1 30 MHz. Total wavelength refers to a single wire dipole in freespace and is theoretical. 1/2 wavelength = combined length of both halves of a wire dipole antenna. 1/4 wavelength = total length of each half of the dipole antenna or can be used to determine the total length of 1/4 wave vertical antenna. In general, you should make the antenna a bit longer so that experimental tuning of the antenna can be done. You may require more length or have to prune off some wire on each half of the dipole to get a low SWR at the desired frequency of operation.