US/Canadian Standard Size Inside Diameter in millimeters Inside Circumference in millimeters Inside Diameter in inches Inside Circumference in inches
5 15.7 49 0.618 1.941
5 1/2 16.1 50.2 0.634 1.992
6 16.51 51.5 0.65 2.042
6 1/2 16.92 52.8 0.666 2.092
7 17.32 54 0.682 2.146
7 1/2 17.73 55.3 0.698 2.196
8 18.13 56.6 0.714 2.249
8 1/2 18.54 57.8 0.73 2.3
9 18.95 59.1 0.746 2.35
9 1/2 19.35 60.3 0.762 2.4
10 19.76 61.6 0.778 2.463
10 1/2 20.17 62.8 0.794 2.504
11 20.57 64.1 0.81 2.567
11 1/2 20.98 66 0.826 2.608
12 21.39 67.3 0.842 2.658