Ring size 63
Updated: 14 July 2026
Ring size 63 means an inside circumference of 63 mm. The inside diameter is 20.1 mm, which is about US 10.5 and UK U. In Europe the number on the ring is the circumference in millimeters, so there is nothing to convert.
Size 63 and the sizes either side
| Size (circumference) | Diameter | US | UK |
|---|---|---|---|
| 61 mm | 19.4 mm | US 9.5 | UK T |
| 62 mm | 19.7 mm | US 10 | UK T |
| 63 mm | 20.1 mm | US 10.5 | UK U |
| 64 mm | 20.4 mm | US 11 | UK V |
| 65 mm | 20.7 mm | US 11 | UK W |
Where the 20.1 mm diameter comes from
Circumference and diameter are linked by pi. Divide the circumference by 3.1416 and you get the diameter:
63 mm divided by 3.1416 is 20.1 mm.
It works the other way around too. If you measured a ring and read 20.1 mm inside diameter, multiply that by 3.1416 and you are back at 63 mm, which is size 63.
Is 63 really your 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.
If 63 does not fit
One size down is 62 mm circumference (19.7 mm diameter), one size up is 64 mm (20.4 mm). One row is one millimeter of circumference, which is roughly a third of a millimeter in diameter.
Whether 63 fits you depends on the ring as well, for example on how wide the band is. Measure again and have a jeweler check the size if the ring is expensive.
Common questions
What does ring size 63 mean?
Ring size 63 means 63 mm inside circumference. The inside diameter is 20.1 mm.
What is ring size 63 in US sizes?
Size 63 is about US 10.5. US sizes run in half steps, so the conversion rarely lands on a round number.
What diameter goes with ring size 63?
20.1 mm. You get it by dividing the 63 mm circumference by 3.1416.