Buying hats online is not the easiest thing in the world to do.
Thats why, here at Tilleyshop.com we think we've got the answer !

Measure your head, so at least you have a rough idea of the size required.
Order that size and also one size either side, eg your head is a size 7 1/4, so order
7 1/4, 7 1/8 and a 7 3/8.
Yes... we know... thats 3 hats that you have to pay for, but you can try them, then return the two that dont fit. All we ask is that ALL tags and labels are still left on and the hat has only been used to try it on indoors.

This must be THE simplest way to buy Online !