To re-enforce this, I bought a large icon in June. It was pretty snug then. With the use from then to now, it packed down and it slides a bit too much. Should have gone medium. Expect the helmet to pack down a bit after some use.Also, if you happen to be right on the edge of two sizes (IE - you could fit a Med snug, or a large with just a little room) go for the smaller size.
Tighter is better than looser.
As for where to measure your noggin, look here:Nice clip and good advice, but not very specific. Nice would have been how and where to measure your noggin? What sizes should be a starting spot compared to measurements?
I would go to the local shop here but I have found them a little less than helpful AFTER you buy your bike. (While shopping for a bike the whole shop is helpful as can be.)
lolz cuz AGV > Icon, u know that!I used to wear a large Icon thinking it was perfect until I went to my medium AGV