I get a lot of people ask about hat measurements. I’ve made a little chart with the sizes I use to help you all out. Even if you don’t design your own hats these measurements are helpful for checking fit of hats made from patterns when you don’t have a live model.
I’ve made so many hats I pretty much have these memorized. Some people might use slightly different measurements. I know there’s a lot of different lengths out there but these have served me well over the years. I like a length that covers the ears well.