Inner Diameter (mm) Inner Circumference (mm) US/Canada Sizes Australian/British Sizes
15.7 49.3 5 J 1/2
15.9 49.9 5 1/4 K 1/4
16.1 50.6 5 1/2 L
16.3 51.2 5 3/4 L 1/4
16.5 51.9 6 M
16.7 52.5 6 1/4 M 1/2
16.9 53.2 6 1/2 N
17.1 53.8 6 3/4 N 1/2
17.3 54.4 7 O
17.5 54.8 7 1/4 O 1/2
17.8 55.8 7 1/2 P
17.9 56.5 7 3/4 P 1/2
18.2 57.2 8 Q
18.4 57.7 8 1/4 Q 1/2
18.5 58.2 8 1/2 Q 3/4
18.7 58.7 8 3/4 R 1/4
18.9 59.3 9 R 3/4
19.2 60.4 9 1/4 S 1/4
19.4 60.9 9 1/2 S 3/4
19.6 61.6 9 3/4 T 1/4
19.8 62.3 10 T 1/2
20.0 62.9 10 1/4 U
20.2 63.5 10 1/2 U 1/2
20.4 64.2 10 3/4 V 1/4
20.7 64.9 11 V 1/2
20.8 65.5 11 1/4 W 1/4
21.1 66.2 11 1/2 W 3/4
21.2 66.7 11 3/4 X 1/4
21.5 67.5 12 Y
21.7 68.1 12 1/4 Y 1/2
21.9 68.8 12 1/2 Z
22.1 69.4 12 3/4 Z 1/2
22.3 70.2 13 Z+1
22.7 71.3 13.5 Z+1.5
23.1 72.5 14 Z+3
23.4 73.5 14.5 Z+4
23.8 74.8 15 Z+5
24.2 76.1 15.5 Z+6
24.6 77.4 16 Z+7