18 Vents Sports Cycling Ultralight Helmet with Visor Mountain Road Bicycle Helmet Vent qty: 18 vents Material: EPS & PC Head width: 18cm / 7.1in Head circumference: 54~64cm / 21.2~25.2in Item size: Approx. 27 * 21 * 12cm / 10.6 * 8.3 * 4.7in