I agree with everyone that it's one of those things that is extremely variable, probably much more so than overall penis size or width. Mine is about the same width as the rest of my penis, except it gets a bit thicker at the very base. I know that the size of my head depends heavily upon just how hard I am. For brief periods at the height of arousal, mine gets pretty big and rock hard, but, usually, even when I have an erection, it's a bit less engorged than my shaft. As far as I know that description that I just gave of myself approximates the average reasonably well, as far as relative size goes.