Ring size converter
| US | UK / AU | EU / ISO | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 3 | G | 44 | 14.1 | 44.2 |
| 3.5 | H | 45 | 14.5 | 45.5 |
| 4 | I | 47 | 14.9 | 46.8 |
| 4.5 | J | 48 | 15.3 | 48.0 |
| 5 | K | 49 | 15.7 | 49.3 |
| 5.5 | L | 51 | 16.1 | 50.6 |
| 6 | M | 52 | 16.5 | 51.9 |
| 6.5 | N | 53 | 16.9 | 53.1 |
| 7 | O | 54 | 17.3 | 54.4 |
| 7.5 | P | 56 | 17.7 | 55.7 |
| 8 | Q | 57 | 18.1 | 57.0 |
| 8.5 | R | 58 | 18.5 | 58.2 |
| 9 | S | 60 | 18.9 | 59.5 |
| 9.5 | T | 61 | 19.4 | 60.8 |
| 10 | U | 62 | 19.8 | 62.1 |
| 10.5 | V | 63 | 20.2 | 63.3 |
| 11 | W | 65 | 20.6 | 64.6 |
| 11.5 | X | 66 | 21.0 | 65.9 |
| 12 | Y | 67 | 21.4 | 67.2 |
| 12.5 | Z½ | 68 | 21.8 | 68.5 |
| 13 | Z+1 | 70 | 22.2 | 69.7 |
Measure a ring you already own
Measure the inside of the ring, edge to edge, in millimetres.
Sizes vary by brand. UK letter sizes are rounded to the nearest half letter, and some jewellers' charts differ by half a size.
How to measure your ring size
With a ring you own
Measure the inside diameter of a ring that fits the right finger, edge to edge, and enter it above.
With string or paper
- Wrap a thin strip of paper or string around the base of your finger.
- Mark where it overlaps, then measure the length in millimetres. That's your circumference.
- Find the nearest circumference in the chart. The EU size is the circumference rounded to the nearest millimetre.
Fingers are slightly bigger at the end of the day and in warm weather. If you're between sizes, choose the larger one, especially for wide bands.
How ring sizes compare
- US and Canada use numbers, usually from 3 to 13 in half or quarter sizes. Each full size adds about 0.8 mm of diameter.
- UK, Ireland and Australia use letters from A to Z. Each letter adds about 1.25 mm of circumference.
- EU sizes follow ISO 8653: the size is the inside circumference in millimetres.
How this converter works
Inner diameter (mm) = 11.63 + 0.8128 × US size. Circumference is the diameter × π, which gives the EU / ISO size. UK letters are worked out from the circumference, with M at about 51.9 mm.
Frequently asked questions
What is a US size 7 ring in mm?
A US 7 ring has an inner diameter of about 17.3 mm and a circumference of about 54.4 mm, which is EU 54 and roughly a UK O.
Is a UK ring size the same as an Australian size?
Yes. The UK, Ireland, Australia and New Zealand all use the same letter sizes.
Selling rings on Shopify? Our ring size chart template includes a ready-made table and measuring guide.