This style of hat is the "trilby", and the front brim is about 6cm.
The hat head-size is 58cm which fits *most people. (If you're not sure, grab a tape measure and wrap it around your head.) The shape is lovely, not too high too flat etc. It's a gorgeous one to wear.
(Please note that hats can not be exchanged due to hygiene purposes, and also mailing hats back and forth can be an expensive exercise because they're in a box.)