7-3/8 is considered a “large” hat size. I either need to use a hat stretcher to fit in one or purchase a larger size. But the diameter of your head tells only half the story, people in my family tend to have tall foreheads as well. We also have what is called a “double crown” not referring to an additional swirl in our hair, but the back of our heads go up, back and out more than other people's heads.
Our heads do not look hydrocephalic although people who have made jokes about my head have used that term incorrectly. I do not actually look strange; I just have a head that is larger than most people's.
Mine goes all the way to the back of my neck....................