Measure your head
Measuring for your head size is both an art and a science. You can use a tape measure (or a length of string that you will have to hold up to a tape measure) to determine the length. Place the string or tape around your head about 1/8" above your ear, across the mid-forehead, completely circling your head. Hold the tape firmly, but not too tightly. Basically you need to measure your head exactly where the hat will sit. If your measurement falls between sizes, choose the next largest size.
Another valid method to determine hat size is to try on a hat and check the size. If you don't own a hat, then try on a random hat next time you are visiting a shop that stocks hats. Sizes, even though they do vary depending on the hat maker, are technically universal. You may refer to the sizing chart below if you need to convert a medium to an actual hat size.
Please understand that hats are not unlike other apparel, in that sizes can vary somewhat from one manufacturer to another. We cannot guarantee that by following these instructions any assurance of a perfect fit.