UK ring sizes use alphabet letters, and US ring sizes use decimal numbers. Converting between them is straightforward once you have a reliable chart, but the tricky part is that the two systems do not always match at exactly the same millimeter step, and some UK half-letter sizes fall between US 0.5 increments.
This guide gives you a full UK to US conversion chart, explains the key differences between the two systems, and covers what to do when a UK letter size has no exact US equivalent.
UK to US Ring Size Conversion Chart
| UK size | US size | EU size | Inner diameter (mm) |
|---|---|---|---|
| F | 3 | 44 | 14.1 |
| G | 3.5 | 45.5 | 14.5 |
| H | 4 | 46.8 | 14.9 |
| I | 4.25 | 47.4 | 15.1 |
| I½ | 4.5 | 48 | 15.3 |
| J | 4.75 | 48.7 | 15.5 |
| J½ | 5 | 49.3 | 15.7 |
| K | 5.25 | 49.9 | 15.9 |
| K½ | 5.5 | 50.6 | 16.1 |
| L | 5.75 | 51.2 | 16.3 |
| L½ | 6 | 51.9 | 16.5 |
| M | 6.25 | 52.5 | 16.7 |
| M½ | 6.5 | 53.1 | 16.9 |
| N | 6.75 | 53.8 | 17.1 |
| N½ | 7 | 54.4 | 17.3 |
| O | 7.25 | 55 | 17.5 |
| O½ | 7.5 | 55.7 | 17.7 |
| P | 7.75 | 56.3 | 17.9 |
| P½ | 8 | 57.2 | 18.2 |
| Q | 8.25 | 57.8 | 18.4 |
| Q½ | 8.5 | 58.5 | 18.6 |
| R | 8.75 | 59.1 | 18.8 |
| R½ | 9 | 59.7 | 19.0 |
| S | 9.25 | 60.4 | 19.2 |
| S½ | 9.5 | 61 | 19.4 |
| T | 9.75 | 61.6 | 19.6 |
| T½ | 10 | 62.2 | 19.8 |
| U | 10.25 | 62.8 | 20.0 |
| U½ | 10.5 | 63.5 | 20.2 |
| V | 10.75 | 64.1 | 20.4 |
| V½ | 11 | 64.8 | 20.6 |
| W | 11.25 | 65.4 | 20.8 |
| W½ | 11.5 | 66 | 21.0 |
| X½ | 12 | 67.2 | 21.4 |
| Z | 13 | 69.7 | 22.2 |
Understanding the Difference Between UK and US Systems
Each full UK letter represents approximately 1.25mm in circumference. US sizes increase by 0.5 steps, which corresponds to about 0.4mm in diameter or roughly 1.3mm in circumference. The two scales are close but not identical at every point, so a clean 1:1 conversion table requires slightly uneven US numbers like 4.25 or 6.75 to represent full UK letters.
In practice, US jewelers stock sizes in 0.5 steps and rarely stock 0.25 increments. If your UK letter converts to a US 0.25 size, round to the nearest 0.5. When in doubt, round up rather than down for daily wear comfort.
Frequently Converted UK to US Sizes
The most commonly searched conversions: UK N½ is US 7. UK L½ is US 6. UK P½ is US 8. UK T½ is US 10. UK J½ is US 5. These five conversions cover the most common jewellery sizing across both countries.
If you are buying a ring in the UK to ship to someone in the US, the safest move is to share the inner diameter in mm with the US jeweler. That measurement is universal and removes any ambiguity about rounding. See our full guide on why ring sizes differ between countries for more on international sizing.
How to Find Your UK Size If You Only Know Your US Size
Find your US size in the second column of the chart above and read across to the UK size on the left. For example, US 7 is UK N½. If you want to double-check your size or measure from scratch, use our ring size calculator to get your result in all systems at once.
For related conversions across other sizing systems, see our US to UK conversion guide and the full US to EU ring size conversion.
FAQ
What is UK ring size N in US?
UK N is US size 6.75 (approximately). If rounding to the nearest standard US half-size, that is US 7.
What is UK L½ in US ring size?
UK L½ is US size 6, with an inner diameter of approximately 16.5mm.
What is UK ring size P in US?
UK P is approximately US 7.75, or US 8 when rounding to the nearest standard half-size.
Is UK ring size the same as US?
No. UK sizes use letters and US sizes use numbers. They measure the same physical dimension (inner diameter in mm) but use different scales.
