21 7/8-23 1/4 * Meets Safety Certification ASTM F 2040, CPSC and EN 1181 * ThinShell EPS foam technology protects the user from sharp and blunt force trauma while sitting as low on your head though so you keep those style points BERN is known for and you have come to expect * Fit system at back of the head customizes to the shape of the head, keeping it stable and comfortable * Compatible Bike/Skate/Warm Weather liner available (sold separately)