| Size | Head circum. (CM) | Head circum. (IN) |
| S | 52 - 55 cm | 20.4 - 21.6" |
| M | 56 - 59 cm | 22 - 23.2" |
| L - XL | 60 - 62 cm | 23.6 - 24.4" |
K2 Thrive Size Guide for Ski Helmets
| Size | Head circum. (CM) | Head circum. (IN) |
| S | 52 - 55 cm | 20.4 - 21.6" |
| M | 56 - 59 cm | 22 - 23.2" |
| L - XL | 60 - 62 cm | 23.6 - 24.4" |