>>5873859that comes with practice, you judge it by eye, you measure it by "heads", with plumblines.
I think I got it from the loomis books but, starting from the top of the skull, counting in heads, remember: chin, nips, navel, nads, 2 heads for knees, 2 heads for feet. those are approximations. then there are others like a foot is about as long as a forearm, etc, you pick these up the more you draw and it becomes second nature, the same way you learnt how to write
