Fitting hats can be quite tricky. I for one hate coming across the "perfect" hat only to find that it's way too big on my little head once I try it on in person. Call me biased, but one of the main reasons I love our hats is because it's REALLY difficult to get the wrong size, and that's because the hats adhere to your head shape quite easily. There is a black, elastic inner lining inside the hat which makes the fit nice and snug. 

Under the "description" of each product you will find two measurements, one is for the "outside rim" and the other for the "inside lining." If you're weary about the sizing to your head I would take a simple tape measure and either measure the circumference of your head (line it slightly above your eyebrows-- where the hat will normally rest) OR if you already have a hat who's fit you love, measure the inner lining of that and compare it to the measurement of the item you're interested in. Trust me when I say I have the hardest time fitting hats, and these adjust super well to a range of head sizes.

Use this link to accurately measure your head size for proper hat fitting.