Runnin' da numbers

One of my customers is a pretty young girl with no hair. I couldn't stand it anymore, and yesterday, I mentioned that there was a competition to design chemo caps. As it turns out, she just finished her chemo....and she let me measure her HEAD! She was pretty interested in what I was doing, and gave me some opinions. So, and please excuse my crappy paint diagram-

I measured point A on myself, and it was roughly 23". (But I have a pumpkin head.) Line D is taken as if the head is 2 dimensional.

Hope it helps!