I've created this page to explain how I've measured my hats :) I use two measurements for accurate sizing, width and ear to ear.

Ear to Ear: This measurement explains where the hat will sit on your ears. To determine this measurement, measure with a soft measuring tape (if you do not have a soft measuring tape use a piece of string, then measure the string) from where you would like the hat to sit on your left ear, across the top of your head, to where it will sit on your right ear. Picture the measuring tape as being a pair of ear muffs.

Width*: Measure horizontally around your head right above your ears. This will determine how wide a hat needs to be.

*With tams and mushroom hats the measurement is a little different since they are worn differently on the head. They are typically worn at an angle from the forehead to the top of the neck so you can tuck in your hair. Measure around your head from your forehead down to your upper neck, and this measurement will be your width.

All of my hats (unless otherwise specified) will stretch a little, so they can fit up to a couple inches larger than the width measurement I give. If you need further explanation feel free to contact me :)