21 - 21 7/8 in * Meets Safety Certification ASTM F 2040, CPSC and EN 1078 * The Lowest Profile Head Protection offering doesn"t look like a spaceship landed on your head like other brands do. * Fit system at back of the head customizes to the shape of the head, keeping it stable and comfortable. * Separate Winter liner can be purchased to convert to either cold weather bike riding, or for skiing/snowboarding