Trouble is with riding hats they are a bit like buying a pair of sandles - The style might be the same but one make is quite different to another. Everyone's head is a slightly different shape too. What you SHOULD do is to go to a shop and try lots of different makes of hat. Only by doing that will you find one that really fits properly.

If you are going to spend a good bit of money on a hat you might as well buy one that really does fit you. It is not a lot of good buying one that doesnt fit. You might have to try on several different makes (all the same size hat) before you get one that really does fit your particular shape of head.