HAT SIZE INCHES CM
7                   22        55.8
7 1/8             22 3/8   56.8
7 1/4             22 3/4   57.7
7 3/8             23 1/8   58.7
7 1/2             23 1/2   59.6
7 5/8             23 7/8   60.6
7 3/4             24 1/4   62
7 7/8             24 5/8   62.5
8                  25         63.5

To figure out your own hat size, measure with tape directly around where the sweetband of the hat will rest.