1. You should start by wrapping a measuring tape around your head about a half-inch above your eyebrows.
2. Since a helmet should be snug so it doesn't pop off if you crash, you need to pull the tape comfortably tight in order to achieve the best results.
3. Make sure you get precise results by measuring two to three times trying to get the same result every time. If you get different measurements take the largest one.

For information concerning helmet sizing click on this link Helmet fitting

ACU Gold Approved for racing - www.acu.org.uk/info/abouttheacu European Safety Standard ECE R22-05 certified