Secret ring sizer
Use this where the other person will not see the screen. A borrowed ring measured by a jeweler is the reliable check. String and paper are guesses. This page does not quote a price.
ISO 8653:2016 defines the size as the inner circumference in millimetres. The US, UK, and Japan columns are calculated from published conventions (US ≈ 36.5 + 2.55 × size mm; UK starts at C = 40 mm and steps 1.25 mm; Japan diameter ≈ 13 + (size − 1) / 3 mm). They are not a shop chart. Confirm with a jeweler.
Print the 50 mm calibration bar. Print at 100% scale.
Diameters printed in the ISO 8653:2016 sample
| ISO size (mm around) | Stick diameter (mm) |
|---|---|
| 41 | 13.05 |
| 51 | 16.23 |
| 61 | 19.42 |
| 71 | 22.6 |
| 76 | 24.19 |
Calculated conversions
| US | Circumference mm | UK | ISO (rounded mm) | Japan |
|---|---|---|---|---|
| 4 | 46.7 | H | 47 | 7 |
| 4.5 | 48 | I | 48 | 8 |
| 5 | 49.3 | J | 49 | 9 |
| 5.5 | 50.5 | K | 51 | 10 |
| 6 | 51.8 | L | 52 | 11 |
| 6.5 | 53.1 | M | 53 | 13 |
| 7 | 54.4 | N 1/2 | 54 | 14 |
| 7.5 | 55.6 | O | 56 | 15 |
| 8 | 56.9 | P 1/2 | 57 | 16 |
| 8.5 | 58.2 | Q 1/2 | 58 | 18 |
| 9 | 59.5 | R 1/2 | 60 | 19 |
| 9.5 | 60.7 | S 1/2 | 61 | 20 |
| 10 | 62 | T 1/2 | 62 | 21 |
| 10.5 | 63.3 | U 1/2 | 63 | 22 |
| 11 | 64.6 | V 1/2 | 65 | 24 |
| 11.5 | 65.8 | W 1/2 | 66 | 25 |
| 12 | 67.1 | X 1/2 | 67 | 26 |