Vintage Ladies Hat, Ladies Sun Hat, Vintage Millenery Ladies Hat

I have a nice old ladies Sun Hat for sale, made by Millenery, In excellent condition, measures about 16" in diameter. The brim is 4 1/2" it says it's a medium but I don't know what that is based on, the opening for your head is about 7" in diameter, has a built on strap you can use or just tuck it in the hat if you don't want to use it.