We are pleased to present the most accurate American to British ring size conversion chart on the web.
| United States and Canada | UK, Australia, New Zealand, South Africa | Diameter Variance (mm) | ||||||
| Circumference (mm) | Diameter (mm) | Ring Size | Circumference (mm) | Diameter (mm) | Ring Size | |||
| 36.5 | 11.6 | 0 | ||||||
| 37.2 | 11.8 | ¼ | 37.5 | 11.9 | A | -0.10 | ||
| 37.8 | 12.0 | ½ | 38.1 | 12.1 | A½ | -0.10 | ||
| 38.5 | 12.2 | ¾ | 38.8 | 12.3 | B | -0.09 | ||
| 39.1 | 12.4 | 1 | 39.4 | 12.5 | B½ | -0.09 | ||
| 39.7 | 12.6 | 1¼ | 40.0 | 12.7 | C | -0.09 | ||
| 40.4 | 12.8 | 1½ | 40.6 | 12.9 | C½ | -0.08 | ||
| 41.0 | 13.1 | 1¾ | 41.3 | 13.1 | D | -0.08 | ||
| 41.6 | 13.3 | 2 | 41.9 | 13.3 | D½ | -0.07 | ||
| 42.3 | 13.5 | 2¼ | 42.5 | 13.5 | E | -0.07 | ||
| 42.9 | 13.7 | 2½ | 43.1 | 13.7 | E½ | -0.07 | ||
| 43.6 | 13.9 | 2¾ | 43.8 | 13.9 | F | -0.06 | ||
| 44.2 | 14.1 | 3 | 44.4 | 14.1 | F½ | -0.06 | ||
| 44.8 | 14.3 | 3¼ | 45.0 | 14.3 | G | -0.05 | ||
| 45.5 | 14.5 | 3½ | 45.6 | 14.5 | G½ | -0.05 | ||
| 46.1 | 14.7 | 3¾ | 46.3 | 14.7 | H | -0.04 | ||
| 46.8 | 14.9 | 4 | 46.9 | 14.9 | H½ | -0.04 | ||
| 47.4 | 15.1 | 4¼ | 47.5 | 15.1 | I | -0.04 | ||
| 48.0 | 15.3 | 4½ | 48.1 | 15.3 | I½ | -0.03 | ||
| 48.7 | 15.5 | 4¾ | 48.8 | 15.5 | J | -0.03 | ||
| 49.3 | 15.7 | 5 | 49.4 | 15.7 | J½ | -0.02 | ||
| 49.9 | 15.9 | 5¼ | 50.0 | 15.9 | K | -0.02 | ||
| 50.6 | 16.1 | 5½ | 50.6 | 16.1 | K½ | -0.01 | ||
| 51.2 | 16.3 | 5¾ | 51.3 | 16.3 | L | -0.01 | ||
| 51.9 | 16.5 | 6 | 51.9 | 16.5 | L½ | -0.01 | ||
| 52.5 | 16.7 | 6¼ | 52.5 | 16.7 | M | 0.00 | ||
| 53.1 | 16.9 | 6½ | 53.1 | 16.9 | M½ | 0.00 | ||
| 53.8 | 17.1 | 6¾ | 53.8 | 17.1 | N | 0.01 | ||
| 54.4 | 17.3 | 7 | 54.4 | 17.3 | N½ | 0.01 | ||
| 55.0 | 17.5 | 7¼ | 55.0 | 17.5 | O | 0.02 | ||
| 55.7 | 17.7 | 7½ | 55.6 | 17.7 | O½ | 0.02 | ||
| 56.3 | 17.9 | 7¾ | 56.3 | 17.9 | P | 0.02 | ||
| 57.0 | 18.1 | 8 | 56.9 | 18.1 | P½ | 0.03 | ||
| 57.6 | 18.3 | 8¼ | 57.5 | 18.3 | Q | 0.03 | ||
| 58.2 | 18.5 | 8½ | 58.1 | 18.5 | Q½ | 0.04 | ||
| 58.9 | 18.7 | 8¾ | 58.8 | 18.7 | R | 0.04 | ||
| 59.5 | 18.9 | 9 | 59.4 | 18.9 | R½ | 0.05 | ||
| 60.2 | 19.1 | 9¼ | 60.0 | 19.1 | S | 0.05 | ||
| 60.8 | 19.4 | 9½ | 60.6 | 19.3 | S½ | 0.05 | ||
| 61.4 | 19.6 | 9¾ | 61.3 | 19.5 | T | 0.06 | ||
| 62.1 | 19.8 | 10 | 61.9 | 19.7 | T½ | 0.06 | ||
| 62.7 | 20.0 | 10¼ | 62.5 | 19.9 | U | 0.07 | ||
| 63.3 | 20.2 | 10½ | 63.1 | 20.1 | U½ | 0.07 | ||
| 64.0 | 20.4 | 10¾ | 63.8 | 20.3 | V | 0.08 | ||
| 64.6 | 20.6 | 11 | 64.4 | 20.5 | V½ | 0.08 | ||
| 65.3 | 20.8 | 11¼ | 65.0 | 20.7 | W | 0.08 | ||
| 65.9 | 21.0 | 11½ | 65.6 | 20.9 | W½ | 0.09 | ||
| 66.5 | 21.2 | 11¾ | 66.3 | 21.1 | X | 0.09 | ||
| 67.2 | 21.4 | 12 | 66.9 | 21.3 | X½ | 0.10 | ||
| 67.8 | 21.6 | 12¼ | 67.5 | 21.5 | Y | 0.10 | ||
| 68.5 | 21.8 | 12½ | 68.1 | 21.7 | Y½ | 0.11 | ||
| 69.1 | 22.0 | 12¾ | 68.8 | 21.9 | Z | 0.11 | ||
| 69.7 | 22.2 | 13 | 69.4 | 22.1 | Z½ | 0.11 | ||
| 70.4 | 22.4 | 13¼ | 70.0 | 22.3 | Z1 | 0.12 | ||
| 71.0 | 22.6 | 13½ | 70.6 | 22.5 | Z1½ | 0.12 | ||
| 71.6 | 22.8 | 13¾ | 71.3 | 22.7 | Z2 | 0.13 | ||
| 72.3 | 23.0 | 14 | 71.9 | 22.9 | Z2½ | 0.13 | ||
| 72.9 | 23.2 | 14¼ | 72.5 | 23.1 | Z3 | 0.13 | ||
| 73.6 | 23.4 | 14½ | 73.1 | 23.3 | Z3½ | 0.14 | ||
| 74.2 | 23.6 | 14¾ | 73.8 | 23.5 | Z4 | 0.14 | ||
| 74.8 | 23.8 | 15 | 74.4 | 23.7 | Z4½ | 0.15 | ||
| 75.5 | 24.0 | 15¼ | 75.0 | 23.9 | Z5 | 0.15 | ||
| 76.1 | 24.2 | 15½ | 75.6 | 24.1 | Z5½ | 0.16 | ||
| 76.8 | 24.4 | 15¾ | 76.3 | 24.3 | Z6 | 0.16 | ||
| 77.4 | 24.6 | 16 | 76.9 | 24.5 | Z6½ | 0.16 | ||
** The diameter variance is the difference between the American Sizes and the British sizes. For example, a US size 4 has a diameter of 14.9mm (rounded up) and a UK H 1/2 has a diameter of 14.9 (rounded down). Because of rounding, the US size 4 is 0.04 mm smaller than the UK H 1/2.