Adult hat sizes are usually determined as follows:
| Hat Size | Circumference | |
| Small | Size 6-3/4 | 21″ |
| Size 6-7/8 | 21-1/2″ | |
| Medium | Size 7 | 22″ |
| Size 7-1/8 | 22-1/2″ | |
| Large | Size 7-1/4 | 22-3/4″ |
| Size 7-3/8 | 23″ | |
| Extra large | Size 7-1/2 | 23-1/2″ |
| Size 7-5/8 | 24″ |
Adult hat sizes are usually determined as follows:
| Hat Size | Circumference | |
| Small | Size 6-3/4 | 21″ |
| Size 6-7/8 | 21-1/2″ | |
| Medium | Size 7 | 22″ |
| Size 7-1/8 | 22-1/2″ | |
| Large | Size 7-1/4 | 22-3/4″ |
| Size 7-3/8 | 23″ | |
| Extra large | Size 7-1/2 | 23-1/2″ |
| Size 7-5/8 | 24″ |
