US and UK ring sizes use completely different systems. The US system uses decimal numbers starting near 3, while the UK system uses letters of the alphabet. That gap causes real confusion when you are buying a ring on an international website, receiving a gift from abroad, or simply shopping a brand that only lists one system.
This guide gives you a full US to UK ring size conversion chart, an inner diameter reference in millimeters, and clear guidance on what to do when your size falls between two letters.
US to UK Ring Size Conversion Chart
| US size | UK size | Inner diameter (mm) | Inner circumference (mm) |
|---|---|---|---|
| 3 | F | 14.1 | 44.2 |
| 3.5 | G | 14.5 | 45.5 |
| 4 | H | 14.9 | 46.8 |
| 4.5 | I½ | 15.3 | 48.0 |
| 5 | J½ | 15.7 | 49.3 |
| 5.5 | K½ | 16.1 | 50.6 |
| 6 | L½ | 16.5 | 51.9 |
| 6.5 | M½ | 16.9 | 53.1 |
| 7 | N½ | 17.3 | 54.4 |
| 7.5 | O½ | 17.7 | 55.7 |
| 8 | P½ | 18.2 | 57.2 |
| 8.5 | Q½ | 18.6 | 58.5 |
| 9 | R½ | 19.0 | 59.7 |
| 9.5 | S½ | 19.4 | 61.0 |
| 10 | T½ | 19.8 | 62.2 |
| 10.5 | U½ | 20.2 | 63.5 |
| 11 | V½ | 20.6 | 64.8 |
| 11.5 | W½ | 21.0 | 66.0 |
| 12 | X½ | 21.4 | 67.2 |
| 13 | Z | 22.2 | 69.7 |
How US and UK Ring Sizes Work Differently
US sizes are numerical and increase in increments of 0.5, where each step represents a change of about 0.4mm in inner diameter. UK sizes use letters, with each full letter representing the same approximate 0.4mm step. The half-letter sizes (like J½ or N½) exist in the UK system to give finer resolution, similar to the 0.5 steps in the US system.
Because both systems are based on the same underlying diameter measurement in millimeters, conversion is reliable. The inner diameter in mm is the common language between all ring sizing systems worldwide.
What to Do When Your Size Falls Between Letters
If your US size converts to a UK half-letter like N½ or Q½ and the jeweler only stocks full letters, you have a choice. Going up one half size is generally better for comfort, especially if you plan to wear the ring daily or if your hands tend to swell.
Wide band rings add another consideration. Because wider bands sit against more finger surface, they feel tighter than narrow rings at the same measured size. For rings wider than 6mm, size up by half a UK letter from what the conversion table shows.
How to Measure Your Ring Size for Cross-Border Shopping
The most reliable starting point for any international purchase is your inner diameter in millimeters. Measure using our ring size calculator, which gives you a calibrated result, then find your measurement in the mm column of the chart above to read across to both the US and UK sizes.
If you already own a ring that fits well, measure its inner diameter directly. Place it on a ruler and read the inside edge in mm. Then match that number to the chart. For more detail on home measurement options, see our guide on how to measure ring size at home.
Common Size Comparisons People Search For
A few conversions come up repeatedly: US size 7 is UK N½, US size 6 is UK L½, and US size 8 is UK P½. These three cover a large portion of women's ring sizes in both countries. For men, US size 10 is UK T½, and US size 11 is UK V½.
If you need to convert in the other direction — from UK back to US — the same table works. Find your UK letter, read across to the US number. For more on international sizing differences, see our full guide on why ring sizes differ between countries.
FAQ
What is US ring size 7 in UK sizing?
US size 7 is UK size N½. The inner diameter is approximately 17.3mm.
What is US ring size 6 in UK sizing?
US size 6 is UK size L½, with an inner diameter of approximately 16.5mm.
Are US and UK ring sizes the same?
No. US sizes use numbers and UK sizes use letters. They are based on the same inner diameter in mm but represented differently. You need a conversion chart or your diameter in mm to match between the two systems.
What is US size 8 in UK?
US size 8 is UK P½, with an inner diameter of around 18.2mm.
How do I convert my UK ring size to US?
Find your UK letter in the chart on this page and read across to the US column. Alternatively, use our free ring size calculator which converts between all major systems automatically.
