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UK ring size O in other sizes
A UK ring size O is US / CA 7¼, Diameter 17.5, Circumference 55.0, EU / ISO 55.
UK / AUO
US / CA7¼
Diameter (mm)17.5
Circumference (mm)55.0
EU / ISO55
Sizes vary by brand. Check the retailer's chart if you are between sizes.
Open full converter →Ring sizes chart
| UK / AU | US / CA | Diameter (mm) | Circumference (mm) | EU / ISO |
|---|---|---|---|---|
| A½ | ½ | 12.0 | 37.8 | 38 |
| B | ¾ | 12.2 | 38.5 | 38 |
| B½ | 1 | 12.4 | 39.1 | 39 |
| C | 1¼ | 12.6 | 39.7 | 40 |
| C½ | 1½ | 12.8 | 40.4 | 40 |
| D | 1¾ | 13.1 | 41.0 | 41 |
| D½ | 2 | 13.3 | 41.6 | 42 |
| E | 2¼ | 13.5 | 42.3 | 42 |
| E½ | 2½ | 13.7 | 42.9 | 43 |
| F | 2¾ | 13.9 | 43.6 | 44 |
| F½ | 3 | 14.1 | 44.2 | 44 |
| G | 3¼ | 14.3 | 44.8 | 45 |
| G½ | 3½ | 14.5 | 45.5 | 45 |
| H | 3¾ | 14.7 | 46.1 | 46 |
| H½ | 4 | 14.9 | 46.8 | 47 |
| I | 4¼ | 15.1 | 47.4 | 47 |
| I½ | 4½ | 15.3 | 48.0 | 48 |
| J | 4¾ | 15.5 | 48.7 | 49 |
| J½ | 5 | 15.7 | 49.3 | 49 |
| K | 5¼ | 15.9 | 49.9 | 50 |
| K½ | 5½ | 16.1 | 50.6 | 51 |
| L | 5¾ | 16.3 | 51.2 | 51 |
| L½ | 6 | 16.5 | 51.9 | 52 |
| M | 6¼ | 16.7 | 52.5 | 52 |
| M½ | 6½ | 16.9 | 53.1 | 53 |
| N | 6¾ | 17.1 | 53.8 | 54 |
| N½ | 7 | 17.3 | 54.4 | 54 |
| O | 7¼ | 17.5 | 55.0 | 55 |
| O½ | 7½ | 17.7 | 55.7 | 56 |
| P | 7¾ | 17.9 | 56.3 | 56 |
| P½ | 8 | 18.1 | 57.0 | 57 |
| Q | 8¼ | 18.3 | 57.6 | 58 |
| Q½ | 8½ | 18.5 | 58.2 | 58 |
| R | 8¾ | 18.7 | 58.9 | 59 |
| R½ | 9 | 18.9 | 59.5 | 60 |
| S | 9¼ | 19.1 | 60.2 | 60 |
| S½ | 9½ | 19.4 | 60.8 | 61 |
| T | 9¾ | 19.6 | 61.4 | 61 |
| T½ | 10 | 19.8 | 62.1 | 62 |
| U | 10¼ | 20.0 | 62.7 | 63 |
| U½ | 10½ | 20.2 | 63.3 | 63 |
| V | 10¾ | 20.4 | 64.0 | 64 |
| V½ | 11 | 20.6 | 64.6 | 65 |
| W | 11¼ | 20.8 | 65.3 | 65 |
| W½ | 11½ | 21.0 | 65.9 | 66 |
| X | 11¾ | 21.2 | 66.5 | 67 |
| X½ | 12 | 21.4 | 67.2 | 67 |
| Y | 12¼ | 21.6 | 67.8 | 68 |
| Y½ | 12½ | 21.8 | 68.5 | 68 |
| Z | 12¾ | 22.0 | 69.1 | 69 |
| Z½ | 13 | 22.2 | 69.7 | 70 |
The highlighted row shows UK O and its equivalents. These are standard conversions used by most retailers; some brands cut larger or smaller, so if you are between sizes, go by your measurements.
Frequently asked questions
What is UK size O in US / CA?
UK ring size O is US / CA 7¼.