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UK ring size guide
UK and Irish ring sizes use letters. Here they are converted to US, EU and Japan, with millimetres.
UK ring sizes to US, EU and Japan
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| UK | US | EU (ISO) | Japan | Diameter mm | Circumference mm |
|---|---|---|---|---|---|
| F | 3 | 44 | 4 | 14.1 | 44.2 |
| G | 3½ | 45 | — | 14.5 | 45.5 |
| H | 4 | 47 | 7 | 14.9 | 46.8 |
| I | 4½ | 48 | 8 | 15.3 | 48.0 |
| J½ | 5 | 49 | 9 | 15.7 | 49.3 |
| K½ | 5½ | 51 | 10 | 16.1 | 50.6 |
| L½ | 6 | 52 | 11 | 16.5 | 51.9 |
| M½ | 6½ | 53 | 13 | 16.9 | 53.1 |
| N½ | 7 | 54 | 14 | 17.3 | 54.4 |
| O½ | 7½ | 56 | 15 | 17.7 | 55.7 |
| P½ | 8 | 57 | 16 | 18.1 | 57.0 |
| Q¼ | 8½ | 58 | 17 | 18.5 | 58.2 |
| R½ | 9 | 60 | 18 | 18.9 | 59.5 |
| S½ | 9½ | 61 | 19 | 19.4 | 60.8 |
| T½ | 10 | 62 | 20 | 19.8 | 62.1 |
| U½ | 10½ | 63 | 22 | 20.2 | 63.3 |
| V½ | 11 | 65 | 23 | 20.6 | 64.6 |
| W½ | 11½ | 66 | 24 | 21.0 | 65.9 |
| X½ | 12 | 67 | 25 | 21.4 | 67.2 |
| Y½ | 12½ | 68 | 26 | 21.8 | 68.5 |
| Z½ (approx.) | 13 | 70 | 27 | 22.2 | 69.7 |
“Women” shows US 3–9 and “Men” US 8–13. These are just filters to shorten the table; anyone can wear any size. Japan: “—” means there is no matching Japanese size.
Half sizes: each UK letter is 1.25 mm of circumference, so a half size is about 0.6 mm. If a ring is between two letters, choose the larger one.
FAQ
How do UK half sizes work?
Each UK letter adds 1.25 mm to the inner circumference, so a half size such as N½ adds about 0.6 mm. Many UK jewelers stock half sizes.
What comes after Z?
Sizes above Z are written Z+1, Z+2 and so on, or Z1, Z2.
What is UK size N in US?
UK N is about US 6¾, and N½ is about US 7.
Sources
How we calculate: the EU size is the inner circumference in millimetres, as defined in ISO 8653:2016. US sizes follow the US scale where each whole size adds 0.032 in (0.8128 mm) to the inner diameter, so diameter = 11.63 mm + 0.8128 mm × US size. UK letters follow British Standard 6820:1987 (size C = 40 mm circumference, each letter adds 1.25 mm). Japanese sizes come from the equivalency table on Wikipedia (Japanese sizes are whole numbers that do not follow a straight formula, so they are rounded to the nearest size). Sources: ISO 8653:2016, Ring size (Wikipedia), equivalency table, Larson Jewelers conversion chart. Charts from different jewelers can round slightly differently, so for an important ring check with the jeweler.
Find your size on screen
Calibrate with a bank card, lay a ring on the screen and read the size in four systems.
Find your size on screen