In general, the Smith Forefront 2 MIPS Helmet can fit large heads with a circumference of up to 62 centimeters. For additional reference, here are the size offerings along with their corresponding measurements: Small runs between 51 and 55 centimeters, Medium runs between 55 and 59 centimeters, while Large runs between 59 and 62 centimeters. At the moment, the Forefront 2 does not offer extra-large sizes beyond 62 centimeters.