Size Diameter (mm) Circum. (mm)
12 16.5 51.8
14 17.2 54.0
16 17.8 55.9
18 18.5 58.1
20 19.2 60.3
22 19.8 62.2
24 20.6 68.7

All measurements are approximate. If your measurement falls between two sizes, we recommend choosing the larger size for a more comfortable fit.