UK to US ring size converter
To convert a UK ring size to US, you translate a letter (A to Z) into a number. UK sizes rise by roughly 1.25 mm of inner circumference per letter, so a UK L is about a US 6 and a UK N½ is a US 7. Pick your UK letter below to see the exact US equivalent.
Quick answer
A UK N½ is 7 in US (about 54.4 mm inner circumference). Use the converter for your exact size, or the chart below for the full range.
Between two sizes? Size up for a comfortable fit, see how to measure accurately.
UK → US at a glance
- H½ = 4
- J½ = 5
- L½ = 6
- N½ = 7
- P½ = 8
- R½ = 9
- T½ = 10
- V½ = 11
UK to US ring size chart
| UKUK / AU | USUS / Canada | mmCircumference | mmDiameter |
|---|---|---|---|
| H½ | 4 | 46.7 | 14.9 |
| I½ | 4½ | 48.0 | 15.3 |
| J½ | 5 | 49.3 | 15.7 |
| K½ | 5½ | 50.5 | 16.1 |
| L½ | 6 | 51.8 | 16.5 |
| M½ | 6½ | 53.1 | 16.9 |
| N½ | 7 | 54.4 | 17.3 |
| O½ | 7½ | 55.6 | 17.7 |
| P½ | 8 | 56.9 | 18.1 |
| Q½ | 8½ | 58.2 | 18.5 |
| R½ | 9 | 59.5 | 18.9 |
| S½ | 9½ | 60.7 | 19.3 |
| T½ | 10 | 62.0 | 19.7 |
| U½ | 10½ | 63.3 | 20.1 |
| V½ | 11 | 64.6 | 20.5 |
| W½ | 11½ | 65.8 | 21.0 |
| X½ | 12 | 67.1 | 21.4 |
What your letter actually means
A UK ring size is not an arbitrary code. Size C is defined as 40 mm of inner circumference, and every letter after it adds 1.25 mm. So H is 46.25 mm, M is 52.5 mm, and R is 58.75 mm. Your letter is a measurement written in shorthand.
That is why the conversion to a US number is reliable. Both scales describe the same circle, so once your letter is turned back into millimetres there is only one US size it can be.
Why one letter can look like two US sizes
US sizes step in 2.55 mm and UK letters step in 1.25 mm, so the two grids do not line up neatly. A single letter sometimes sits almost exactly between two US half sizes, and different charts round it in different directions. That is the usual reason two websites disagree by half a size.
Rather than trusting a rounded chart, convert your letter to millimetres first and then to a US size. The converter above does exactly that, which is why it can tell you when your size genuinely falls between two US options instead of silently picking one.
Sizes written with a half
UK sizes are commonly quoted with a half, written as N½ or sometimes N 1/2. The half is a real half letter, not a rounding note, and it matters: half a letter is about 0.6 mm of circumference, which is enough to change how a ring feels over a knuckle.
If a jeweller has written your size by hand, check whether a mark after the letter is a half symbol or a stray pen stroke. Converting N and N½ gives you two different US answers.
Common questions
How do I convert a UK ring size to US?
Enter your UK size in the converter above and read the US result, or find your row in the chart below. Every value is calculated from the ring’s inner circumference, so it works in both directions.
What is a UK N½ in US?
A UK N½ is 7 in US. That ring has an inner circumference of about 54.4 mm.
Related conversions
Or see the full ring size chart.