M SIZE BIKE HELMET:21.6-22.83INCH(55-58CM)L SIZE BIKE HELMET:22.83-24INCH(58-61CM) DKONI adult bike helmet is constructed with a high-quality PC shell and high-density EPS foam meets CPSC 1203 Safety Certified for Bicycle Road Bike, provides excellent shock absorption upon initial impact Cycling Helmet with 15 breathable vents for provide superior comfort for a long ride trips. removable inner pads are easy to wash. DKONI bike helmet for man and women is suit for multi sports, like E-Bikes,cycling,Onewheel,Commuter,skateboarding,skateboard,ebike,scooter,rollerskate,e electric biking, Scooters,MTB,BMX,rollerblade,longboard etc. Adults Men Women,Mens/Womens,man woman, Youth Boys/Girls all perfect fit for DKONI bicycle helmet. DKONI helmet can protect you day and night,USB Rechageable light is easy to detach,flashing in the night.