I usually wear a large hat. I ordered a large in this, and it's too large - should have purchased a medium. There is a cinch on the back to tighten in, but it's not nearly enough to make this snug.  My ears actually fit up inside the hat - it I pull it down too far, it's will cover my eyes. Sow, yea, it's a big fit. The quality is great - covered in the same material as my London Fog rain coat.