US ring size 9 in mm
Updated: 14 July 2026
US ring size 9 is European sizes 59 to 60. The European size is simply the inside circumference in millimeters, here 59 mm at 18.8 mm inside diameter. The US scale counts in its own steps, which is why the two numbers look so different.
US 9 in the conversion chart
| Size (circumference) | Diameter | US | UK |
|---|---|---|---|
| 56 mm | 17.8 mm | US 7.5 | UK P |
| 57 mm | 18.1 mm | US 8 | UK Q |
| 58 mm | 18.5 mm | US 8.5 | UK Q |
| 59 mm | 18.8 mm | US 9 | UK R |
| 60 mm | 19.1 mm | US 9 | UK S |
| 61 mm | 19.4 mm | US 9.5 | UK T |
| 62 mm | 19.7 mm | US 10 | UK T |
Why the two numbers look so different
Europe measures the inside circumference and uses those millimeters as the size. The US scale counts in its own numbers, tied to the inside diameter: one US size up is about 0.8 mm more diameter, which is about 2.5 mm more circumference.
That is why the conversion rarely lands on a round number. US 9 sits at 18.8 mm diameter, which is European 59. When in doubt, trust the measured circumference in millimeters, it is unambiguous.
Measure your own size
These are the reliable ways to measure:
- Take a ring that already fits the right finger, lay it on a ruler and measure the inside diameter from edge to edge.
- Or use a ring sizer, a set of sample rings you try on one by one.
- Or have a jeweler measure your finger.
The string method (wrap a string around the finger and measure its length) is a fallback for when none of the above is possible. It gives you a rough estimate. Measure the finger you want to wear the ring on and remember that the ring also has to pass your knuckle.
The sizes either side
US 8 sits at 57 mm circumference, US 10 at 62 mm. So one whole US size covers more than one European number. If you land between two values, measure again instead of guessing.
Common questions
What is US ring size 9 in EU sizes?
US 9 is European sizes 59 to 60, so 59 mm inside circumference.
What diameter does US 9 have?
About 18.8 mm inside diameter.
What is US 9 in UK ring sizes?
That is the British letter R. The UK uses letters instead of numbers.