Size Charts for K2 Helmets
Adult
| US Size | Inches |
| X-Small | 18 7/8 - 20 1/8 |
| Small | 20 1/2 - 21 5/8 |
| Medium | 22 - 23 1/8 |
| Large | 23 1/2 - 24 |
| X-Large | 24 - 24 3/8 |
Adult
| US Size | Inches |
| X-Small | 18 7/8 - 20 1/8 |
| Small | 20 1/2 - 21 5/8 |
| Medium | 22 - 23 1/8 |
| Large | 23 1/2 - 24 |
| X-Large | 24 - 24 3/8 |