my head size is around 58-59 so I was right on the border of M or L size. I went with a M and it was too tight. Returned it for an L and it was looser but not too jiggly. the remedy protected my noggin from a major crash that cracked it but not my skull. I had a concussion, pulled my shoulder, and apparently knocked out for a bit. whee! good helmet. a bit heavy but I'd carry the weight if I know the protection is there.