how to find out the aperture of an antenna?

Usually how to find out the aperture of an antenna? By measurement or simulation?
Is there somewhere the aperture for frequently used antenna can be found?
I can see the aperture values of some antennas are listed in Wiki, e.g. the aperture for half-wave dipole is 0.1305*lamda^2
but I would like to know the dimension of the aperture, e.g. width*length
this is because this dimension is needed for the calculation of far field condition
Thanks!

You might want to look into radiation patterns and 3db points etc as a definition for 'aperture'. There is lots n lots of publications on this aspect.

But i'm sure you know that already.

cheers!