NOTE:We strongly recommend ordering one size up from the recommended size on the size chart!Gath SFC Surf Convertible Helmet designed for the surf is the lightest helmet available world-wide. Its unique fitting system provides an incredibly snug comfortable suction cap fit idea for punching through waves.Gath ear protectors are easily removed to expose the ears - ideal for hot weather - or easily attached becoming an extension of the helmet shell for added impact protection and extra warmth in cold conditions. Adjustable audio vents allow further flexibility to shut out the cold wind or open to improve hearing.SIZING:Small:Head 21 1/4" to 21 7/8" | 540mm - 555mmAmerican Hat: 6 3/4 to 7Medium:Head 22" to 22 5/8" | 560mm - 575mmAmerican Hat: 7 to 7 1/4Large:Head 22 7/8" to 23 1/4" | 580mm - 590mmAmerican Hat: 7 1/4 to 7 3/8X-Large:Head 23 3/8" to 24" | 595mm - 610mmAmerican Hat: 7 3/8 to 7 5/82X-Large:Head 24" to 24 3/8" | 610mm - 620mmAmerican Hat: 7 3/4 to 7 7/83X-Large:Head 24 3/8" to 24 7/8" | 620mm - 630mmAmerican Hat: 7 7/8 to 8