Size guide

Diameter In mm Circumference In mm Australia & Newzealand USA & Canada
15.1 47.43 I 4 1/2
15.5 48.69 J 4 3/4
16 50.26 K 5 1/4
16.3 51.2 L 5 3/4
16.7 52.46 M 6 1/4
17.1 53.72 N 6 3/4
17.4 54.66 O 7 1/4
17.7 55.6 P 7 3/4
18.1 56.86 Q 8 1/4
18.5 58.11 R 8 3/4
18.9 59.37 S 9 1/4
19.4 60.94 T 9 3/4
19.8 62.2 U 10 1/4
20.3 63.77 V 10 3/4