Ring size chart: US, UK, ISO and more
US 7 is a ring 17.3 mm across inside and 54.4 mm round, which is UK N½ and ISO 54. This chart lists every half US size from 3 to 14 with its inside diameter and circumference in millimetres and the nearest size in the other systems.
Ring size chart
| US / Canada | Inside Ø mm | Circumference mm | UK / Australia | ISO / Europe | Switzerland, Italy, Spain | Japan | Hong Kong, China |
|---|---|---|---|---|---|---|---|
| 3 | 14.1 | 44.2 | ≈ F½ | ≈ 44 | ≈ 4 | ≈ 4 | ≈ 6 |
| 3.5 | 14.5 | 45.5 | ≈ G½ | ≈ 45 | ≈ 5 | ≈ 5 | 7 |
| 4 | 14.9 | 46.8 | H½ | ≈ 47 | ≈ 7 | ≈ 7 | 8 |
| 4.5 | 15.3 | 48.0 | I½ | 48 | 8 | 8 | ≈ 9 |
| 5 | 15.7 | 49.3 | J½ | ≈ 49 | ≈ 9 | 9 | ≈ 10 |
| 5.5 | 16.1 | 50.6 | K½ | ≈ 51 | ≈ 11 | ≈ 10 | ≈ 12 |
| 6 | 16.5 | 51.9 | L½ | 52 | 12 | ≈ 12 | ≈ 13 |
| 6.5 | 16.9 | 53.1 | M½ | 53 | 13 | ≈ 13 | 14 |
| 7 | 17.3 | 54.4 | N½ | ≈ 54 | ≈ 14 | 14 | 15 |
| 7.5 | 17.7 | 55.7 | O½ | ≈ 56 | ≈ 16 | ≈ 15 | ≈ 16 |
| 8 | 18.1 | 57.0 | P½ | 57 | 17 | ≈ 16 | ≈ 17 |
| 8.5 | 18.5 | 58.2 | Q½ | ≈ 58 | ≈ 18 | ≈ 18 | ≈ 19 |
| 9 | 18.9 | 59.5 | R½ | ≈ 60 | ≈ 20 | ≈ 19 | ≈ 20 |
| 9.5 | 19.4 | 60.8 | ≈ S½ | ≈ 61 | ≈ 21 | 20 | ≈ 21 |
| 10 | 19.8 | 62.1 | ≈ T½ | 62 | 22 | ≈ 21 | 22 |
| 10.5 | 20.2 | 63.3 | ≈ U½ | ≈ 63 | ≈ 23 | ≈ 22 | ≈ 23 |
| 11 | 20.6 | 64.6 | ≈ V½ | ≈ 65 | ≈ 25 | ≈ 24 | ≈ 24 |
| 11.5 | 21.0 | 65.9 | ≈ W½ | 66 | 26 | 25 | ≈ 26 |
| 12 | 21.4 | 67.2 | ≈ X½ | ≈ 67 | ≈ 27 | ≈ 26 | ≈ 27 |
| 12.5 | 21.8 | 68.5 | ≈ Z | ≈ 68 | ≈ 28 | ≈ 27 | ≈ 28 |
| 13 | 22.2 | 69.7 | ≈ Z+1 | ≈ 70 | ≈ 30 | ≈ 29 | 29 |
| 13.5 | 22.6 | 71.0 | ≈ Z+2 | 71 | 31 | ≈ 30 | ≈ 30 |
| 14 | 23.0 | 72.3 | ≈ Z+3 | ≈ 72 | ≈ 32 | 31 | ≈ 31 |
How to read the chart
Find your size or your measurement in the first columns, then read across. A ring is described by its inside diameter, the straight distance across the hole, or by its inside circumference, the distance round it. The circumference is the diameter times 3.1416.
The sizes in other columns are the closest ones in each system. The scales do not meet exactly, so a US size can fall between two European sizes. The pages for each system show the exact difference.
Questions
What size ring is 17.3 mm?
An inside diameter of 17.3 mm is US 7, UK N½ and ISO 54, with an inside circumference of 54.4 mm.
How do I read a ring size in mm?
A ring size in millimetres is either the inside diameter or the inside circumference. ISO sizes are the circumference in millimetres, so ISO 54 is 54 mm round.
How big is one US ring size?
One whole US size is 0.8 mm of inside diameter, or 2.6 mm of circumference. A half size is half of that.