I've tried a lot of different full faced helmets and this one fits me the best. I always wear a Medium in road/mountain helmets (I'm at the upper end of the sizing range though), but I guess my head is a weird shape because many of the full-faced mediums were just too tight. Specialized Deviant (too tight), Giro Remedy (too tight), SixSixOne (too tight). So I'd try the large size and they were way too big. The Bell Drop in a medium is just right. Way better venting than a SixSixOne and if it were vented like the Deviant, then 5 stars, but it's not quite that luxurious. Great lid.