US to UK Ring Size Converter & Chart
US sizes are numbers; UK sizes are letters. Convert instantly below, then read why the two systems never quite line up — and why millimetres settle every argument.
Last updated: November 2026
Convert US ↔ UK
US to UK chart
| US / Canada | UK / Australia | Diameter (mm) | Circumference (mm) |
|---|---|---|---|
| US 3 | UK F | 14.1 mm | 44.2 mm |
| US 3.5 | UK G | 14.5 mm | 45.5 mm |
| US 4 | UK H½ | 14.9 mm | 46.8 mm |
| US 4.5 | UK I½ | 15.3 mm | 48.0 mm |
| US 5 | UK J½ | 15.7 mm | 49.3 mm |
| US 5.5 | UK K½ | 16.1 mm | 50.6 mm |
| US 6 | UK L½ | 16.5 mm | 51.9 mm |
| US 6.5 | UK M½ | 16.9 mm | 53.1 mm |
| US 7 | UK N½ | 17.3 mm | 54.4 mm |
| US 7.5 | UK O½ | 17.7 mm | 55.7 mm |
| US 8 | UK P½ | 18.1 mm | 57.0 mm |
| US 8.5 | UK Q½ | 18.5 mm | 58.3 mm |
| US 9 | UK R½ | 18.9 mm | 59.5 mm |
| US 9.5 | UK S½ | 19.4 mm | 60.9 mm |
| US 10 | UK T½ | 19.8 mm | 62.1 mm |
| US 10.5 | UK U½ | 20.2 mm | 63.4 mm |
| US 11 | UK V½ | 20.6 mm | 64.6 mm |
| US 11.5 | UK W½ | 21.0 mm | 66.0 mm |
| US 12 | UK X½ | 21.4 mm | 67.2 mm |
| US 12.5 | UK Y½ | 21.8 mm | 68.5 mm |
| US 13 | UK Z½ | 22.2 mm | 69.7 mm |
Honest note on charts: Ring size charts vary by up to half a size between jewellers. Always confirm your size in millimetres — inner diameter or circumference — with the jeweller you are buying from before you order.
The letter system, explained
The UK (with Ireland, Australia, New Zealand and South Africa) sizes rings with letters A to Z, plus half letters like N½. Each full letter step is about 1.25 mm of circumference, while a full US size is about 2.55 mm — roughly two letter steps. That mismatch is why conversions land on half letters and why two jewellers' charts can differ by half a letter: both are rounding the same millimetres differently. When it matters, quote the mm. For other systems see the full converter and complete chart.