I, too, have a large cranium and wear a 7 3/4 hat. I am using a Giro Aether in the large size. However, I am also bald so that might be why I can get the helmet comfortably on. It is opened up all the way for the supports and straps. I am able to wear a thin lycra head cover under for sun protection. Again, if you got the head size and hair as well, it may be undersized for you.