US to UK ring size converter
US and UK ring sizes use completely different scales. The US system is numeric with half sizes, while the UK, Ireland, Australia and New Zealand use letters from A to Z. A US 7, for example, is a UK N½. Enter a size below to convert either direction, or use the full chart underneath.
Quick answer
A US 7 is N½ in UK (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.
US → UK at a glance
- 4 = H½
- 5 = J½
- 6 = L½
- 7 = N½
- 8 = P½
- 9 = R½
- 10 = T½
- 11 = V½
US to UK ring size chart
| USUS / Canada | UKUK / AU | mmCircumference | mmDiameter |
|---|---|---|---|
| 4 | H½ | 46.7 | 14.9 |
| 4½ | I½ | 48.0 | 15.3 |
| 5 | J½ | 49.3 | 15.7 |
| 5½ | K½ | 50.5 | 16.1 |
| 6 | L½ | 51.8 | 16.5 |
| 6½ | M½ | 53.1 | 16.9 |
| 7 | N½ | 54.4 | 17.3 |
| 7½ | O½ | 55.6 | 17.7 |
| 8 | P½ | 56.9 | 18.1 |
| 8½ | Q½ | 58.2 | 18.5 |
| 9 | R½ | 59.5 | 18.9 |
| 9½ | S½ | 60.7 | 19.3 |
| 10 | T½ | 62.0 | 19.7 |
| 10½ | U½ | 63.3 | 20.1 |
| 11 | V½ | 64.6 | 20.5 |
| 11½ | W½ | 65.8 | 21.0 |
| 12 | X½ | 67.1 | 21.4 |
Why the two scales look nothing alike
The US scale is a number line with no obvious starting point, while the UK scale is the alphabet. They look unrelated, but underneath they measure exactly the same thing: the distance around the inside of the band. That is why converting between them is exact arithmetic rather than a rough guess.
The UK letters come from a British Standard that fixes size C at 40 mm of inner circumference and adds 1.25 mm for every letter after it. The US scale starts at a different point and climbs in steps of 2.55 mm. Once you know both anchors, every letter has a precise numeric twin.
One US half size is almost exactly one UK letter
This is the shortcut worth remembering. A full US size is 2.55 mm of circumference, so a US half size is about 1.275 mm. A single UK letter is 1.25 mm. The two steps differ by just 0.025 mm, which is far finer than anyone can feel.
In practice that means moving up a half size in the US is the same as moving up one letter in the UK. A US 7 is a UK N½, so a US 7½ is a UK O½ and a US 6½ is a UK M½. The tiny difference does accumulate over many steps, so use the chart rather than counting letters if you are far from a size you already know.
Ordering from a UK jeweller
British and Irish jewellers will quote you a letter, sometimes with a half marked as ½. If a shop gives you a letter and no half, ask whether they measured on a mandrel or with a sizing ring set, because the two can round differently at the edges.
If your converted size lands between two letters, take the larger one. A ring that is slightly loose can be made smaller far more easily than a tight one can be stretched, and plain bands resize more readily than eternity rings or anything in tungsten or ceramic.
Common questions
How do I convert a US ring size to UK?
Enter your US size in the converter above and read the UK 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 US 7 in UK?
A US 7 is N½ in UK. That ring has an inner circumference of about 54.4 mm.
Related conversions
Or see the full ring size chart.