Find Your Right Motorcycle Helmet Size Our new sizes correspond to the following head circumferences: M= 21.65 - 22.84 in (55-58 cm) L = 23.23 - 24.41 in (59-62 cm) TIPS: 1. The head circumference is measured in inches at the widest point approx. 2 cm above the ears using a measuring tape. 2. Alternatively, the circumference can also be measured with the help of a cord/leash or similar and transferred to a tape measure/inch stick. 3. If the result is between two sizes, you should choose the larger size.