US and Canada ring sizes
US and Canadian ring sizes run in quarter steps: size 0 is 11.63 mm across inside and each whole size adds 0.8128 mm of diameter, so US 7 is 17.3 mm across and 54.4 mm round.
Defined by a published formula; the standard text was not read.
Where it is used: United States, Canada
US and Canada size table
| US and Canada size | Inside Ø mm | Circumference mm | Nearest US | Nearest UK | Nearest ISO |
|---|---|---|---|---|---|
| 3 | 14.1 | 44.2 | 3 | ≈ F½ | ≈ 44 |
| 3.5 | 14.5 | 45.5 | 3.5 | ≈ G½ | ≈ 45 |
| 4 | 14.9 | 46.8 | 4 | H½ | ≈ 47 |
| 4.5 | 15.3 | 48.0 | 4.5 | I½ | 48 |
| 5 | 15.7 | 49.3 | 5 | J½ | ≈ 49 |
| 5.5 | 16.1 | 50.6 | 5.5 | K½ | ≈ 51 |
| 6 | 16.5 | 51.9 | 6 | L½ | 52 |
| 6.5 | 16.9 | 53.1 | 6.5 | M½ | 53 |
| 7 | 17.3 | 54.4 | 7 | N½ | ≈ 54 |
| 7.5 | 17.7 | 55.7 | 7.5 | O½ | ≈ 56 |
| 8 | 18.1 | 57.0 | 8 | P½ | 57 |
| 8.5 | 18.5 | 58.2 | 8.5 | Q½ | ≈ 58 |
| 9 | 18.9 | 59.5 | 9 | R½ | ≈ 60 |
| 9.5 | 19.4 | 60.8 | 9.5 | ≈ S½ | ≈ 61 |
| 10 | 19.8 | 62.1 | 10 | ≈ T½ | 62 |
| 10.5 | 20.2 | 63.3 | 10.5 | ≈ U½ | ≈ 63 |
| 11 | 20.6 | 64.6 | 11 | ≈ V½ | ≈ 65 |
| 11.5 | 21.0 | 65.9 | 11.5 | ≈ W½ | 66 |
| 12 | 21.4 | 67.2 | 12 | ≈ X½ | ≈ 67 |
| 12.5 | 21.8 | 68.5 | 12.5 | ≈ Z | ≈ 68 |
| 13 | 22.2 | 69.7 | 13 | ≈ Z+1 | ≈ 70 |
| 13.5 | 22.6 | 71.0 | 13.5 | ≈ Z+2 | 71 |
About US and Canada sizes
The US and Canadian system is used in the US and Canada. Its numbered sizes move in quarter steps. For example, US 7 corresponds to an inside diameter of 17.3 mm and a circumference of 54.4 mm. The diameter measures across the inside of the ring; the circumference measures around it.
The table pairs US sizes with UK, ISO, Swiss, Italian, Spanish, Japanese, Hong Kong, and Indian sizes. These labels follow different conventions, so a matching number or letter does not mean the systems use the same scale. UK letters printed alongside US sizes can be half a letter off, so use the measurements when comparing.
Use the table to compare a size with its inside diameter and circumference, then check the shop’s own chart before buying. If you have a ring that fits, measure its inside diameter and compare it with the table. The Ring Size Converter can help compare labels, and the Printable Ring Sizer can help you check your size.
Sources
- Ring size (Wikipedia) Checked November 10, 2026
- How to Determine Ring Size: Tips and Ring Size Chart (GIA (Gemological Institute of America)) Checked November 10, 2026