Tell you what I did.
I spoke with the guys in Ca. @ Nexx-Usa. I wasn't sure of my size, and I paid up front for the X-30 to be shipped to me in size med. (I didn't know any bike shops in my area that carried their helmet let alone even heard of the helmet.) After I fiqured that the medium was the wrong size I ordered the large, which fits me fine.
My first helmet is a Shoei 1000
in large. Love the Shoei but, my head is oval and I end up with a crease on top of my far head from the padding it takes a couple of hours fot it to disappear.
My Nexx helmet I bought for the summer. I hope to land a Roof Boxer V8 some day, just to try it for size.
Call them at Nexx they are easy to work with. By the way,Nexx asked if I was interested in reping them in my state, I declined as I already run a business 12/6 Good luck, with your new helmet.
www.Revzilla.com which is in Phila. will soon be carring the Nexx helmet line, ask for Marcus tell him your a Spyder rider and was refered by me.