Dipole Antenna Length

The length of a dipole antenna 'L' is calculated as follows .

L = (Wavelength in free space /2) * (ratio of velocity of the electromagnetic waves in the antenna metal to free space.)

For many good conductors like copper, aluminum etc. it can be approximated as 95% of the velocity of light in free space. It is assumed here the diameter of the conductor is negligible in comparison with free space wavelength .

So 'L' =  Wavelength in free space * 0.95/2

Hope this helps.