Believe it or not, it depends on the frequency of your favorite radio station.

The optimum antenna length can be determined by using one of these formulas:

To figure a quarter-wavelength antenna in feet, divide 234 by the frequency in MHz.

To figure a half-wavelength antenna in feet, divide 468 frequency in MHz.

To figure a full-wavelength antenna in feet, divide 936 by the operating frequency in MHz.

Convert to inches using the usual formula.

A quarter-wavelength antenna is the minimum-size antenna. A half-wavelength (or greater) provides better reception. Five full wavelengths provide the optimum antenna length for any given frequency. If you have the room.