| Circumference, mm | Ring diameter, mm | USA, Canada | Europe | England, Ireland, Austria, New Zeland | Asia (India, China, Japan) & South America | Rest of Europe (Italy, Spain, Netherlands, Switzerland) |
| 50.3 | 16 | 5 1/2" | 50.5 | K 1/2 | 10 | 10.5 |
| 51.8 | 16.5 | 6" | 52 | L 1/2 | 11 | 12 |
| 53.4 | 17 | 7" | 53.5 | N | 13-14 | 13.5 |
| 55 | 17.5 | 7 1/2" | 55 | O | 15 | 15 |
| 56.5 | 18 | 8" | 56.5 | P 1/2 | 16 | 16.5 |
| 58.1 | 18.5 | 8 1/2" | 58 | Q 1/2 | 17 | 18 |
| 59.7 | 19 | 9" | 59.5 | R 1/2 | 18 | 19.5 |
| 61.3 | 19.5 | 9 1/2" | 61.5 | T | 19-20 | 21.5 |
| 62.8 | 20 | 10" | 63 | U | 21 | 23 |
| 64.4 | 20.5 | 11" | 64.5 | V 1/2 | 23 | 24.5 |
| 66 | 21 | 11 1/2" | 66 | X | 24-25 | 26 |
| 67.5 | 21.5 | 12" | 67.5 | Y | 25-26 | 27.5 |
| 69.1 | 22 | 12 1/2" | 69 | Z 1/2 | 26-27 | 29 |
| 70.7 | 22.5 | 13" | 70.5 | Z 1 | 30.5 | |
| 72.3 | 23 | 13 1/2" | 72.5 | Z 3 | 32.5 |
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