Size M (55-56 CM,21.7/22.0 Inch); Helmet comes with LED Tail Light; Two AAA batteries Required (Not included in the helmet); Advanced Dual Lens & Quick Release Buckle Design; Light Weight Durable Aerodynamic Thermoplastic Alloy Shell; Beautiful Glossy UV Protective Finish; Removable and Washable Padding; DOT Approved; Meets Federal Motor Vehicle Safety Standard 218 (FMVSS 218); Helmet Size Chart

S 53-54 CM 20.9/21.3 Inch
M 55-56 CM 21.7/22.0 Inch
L 57-58 CM 22.4/22.8 Inch
XL 59-60 CM 23.2/23.6 Inch

Helmet Size Tips

(1)Wrap a measuring tape around your head about a half-inch above eyebrows
(2)Take measurement two to three times to pick the largest one.