It's suppose to be one size fits all. First off I have a very small head, I usually have to shop boys hats to find something that fits. So this for me was perfect when I first put it on, my concern was that probably after a few months it'll stretch out, well I didn't have to worry about that, it doesn't take a few months. Literally hours after having it on, I took it off and on a few times but noticed that it felt bigger and bigger, and that's exactly what happened. After not even wearing it all day, it stretch to a couple size bigger. No I didn't pull on it or stretch it out in anyway. With just putting it on and taking it off a few times, it stretch to the point of a passing wind blew it off my head. Do not recommend