Complete reference chart for ring sizes in millimeters, with both inner diameter and circumference mapped to US, UK, EU, and Japanese sizing systems. This chart follows the ISO 8653 standard for ring sizing. Enter your measurement in millimeters to find your size in any system, or browse the full table below.
Measure in the afternoon when fingers are at their largest. Finger size changes with temperature and time of day.
| US | UK | EU | JP | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.0 | 44.0 |
| 3.5 | G | 45.5 | 5 | 14.4 | 45.2 |
| 4 | H | 46.5 | 7 | 14.8 | 46.5 |
| 4.5 | I | 47.8 | 8 | 15.2 | 47.8 |
| 5 | J | 49 | 9 | 15.6 | 49.0 |
| 5.5 | K | 50.3 | 10 | 15.9 | 50.3 |
| 6 | L | 51.5 | 12 | 16.5 | 51.8 |
| 6.5 | M | 52.8 | 13 | 16.9 | 53.1 |
| 7 | N | 54 | 14 | 17.3 | 54.3 |
| 7.5 | O | 55.3 | 15 | 17.7 | 55.6 |
| 8 | P | 56.6 | 16 | 18.1 | 56.9 |
| 8.5 | Q | 57.8 | 17 | 18.5 | 58.1 |
| 9 | R | 59 | 18 | 18.9 | 59.3 |
| 9.5 | S | 60.3 | 19 | 19.2 | 60.6 |
| 10 | T | 61.6 | 20 | 19.8 | 62.1 |
| 10.5 | U | 62.8 | 22 | 20.2 | 63.4 |
| 11 | V | 64 | 23 | 20.6 | 64.6 |
| 12 | X | 66.6 | 25 | 21.3 | 66.9 |
| 13 | Z | 69.1 | 27 | 22.0 | 69.1 |
ISO 8653 (also EN 28653) defines ring sizes by the inner circumference in millimeters. This is the basis for EU ring sizing and is the most internationally consistent method.
Either works, but circumference is more practical for home measurement (using string or paper strip). Our chart includes both for your convenience.
The string method is accurate to within about 1-2mm if done carefully. For critical purchases like engagement rings, we recommend confirming with a jeweler\'s ring mandrel.
A 17mm inner diameter corresponds to approximately a US 6.5 to 7, UK M to N, or EU 53-54.
Fingers tend to swell slightly throughout the day, so measuring in the late afternoon or evening generally gives the most representative result. Avoid measuring when your hands are very cold (fingers shrink) or right after exercise (fingers swell temporarily). For the most reliable reading, measure at two different times and use the larger value.