| Inner Circumference | Ring Sizes | Ring Diameter | ||||
| Inch | mm | cm | U.S.A. | U.K. & Australia | Inch | mm |
| 1.85 | 47 | 4.7 | 4 | H | 0.586 | 14.88 |
| 1.89 | 48 | 4.8 | 4 1/2 | I | 0.602 | 15.29 |
| 1.93 | 49 | 4.9 | 5 | J | 0.619 | 15.72 |
| 1.97 | 50 | 5.0 | 5 1/2 | K | 0.635 | 16.13 |
| 2.05 | 52 | 5.2 | 6 | L | 0.652 | 16.56 |
| 2.09 | 53 | 5.3 | 6 1/2 | M | 0.668 | 16.97 |
| 2.13 | 54 | 5.4 | 7 | N | 0.685 | 17.40 |
| 2.17 | 55 | 5.5 | 7 1/2 | O | 0.701 | 17.80 |
| 2.24 | 57 | 5.7 | 8 | P | 0.717 | 18.21 |
| 2.28 | 58 | 5.8 | 8 1/2 | Q | 0.734 | 18.64 |
| 2.36 | 60 | 6.0 | 9 | R | 0.750 | 19.05 |
| 2.40 | 61 | 6.1 | 9 1/2 | S | 0.767 | 19.48 |
| 2.44 | 62 | 6.2 | 10 | T | 0.783 | 19.89 |
| 2.48 | 63 | 6.3 | 10 1/2 | U | 0.800 | 20.32 |
| 2.52 | 64 | 6.4 | 11 | V | 0.816 | 20.73 |
| 2.56 | 65 | 6.5 | 11 1/2 | W | 0.833 | 21.16 |
| 2.64 | 67 | 6.7 | 12 | X | 0.849 | 21.57 |
| 2.68 | 68 | 6.8 | 12 1/2 | Y | 0.866 | 22.00 |
| 2.71 | 69 | 6.9 | 13 | Z | 0.882 | 22.40 |