here you go
http://www.fmhelmets.co.uk/sizing.html

i'd still advise to try it on or atleast go to a shop try one on for size then buy off the net if you can get it cheaper as even though it's says it's your size it might not fit very well.

also remember make sure it's a real snug fit as with use it'll loosen up and you wont wan't it loose on your head once it gives .

oh and no prob's mate atleast i can give some useful info back at times