US ring size 9

US size 9 has an inside diameter of approximately 18.9 mm and an inside circumference of 59.5 mm.

How to check whether size 9 fits

Measure the inside diameter of a ring that already fits the intended finger. Measure straight across the widest inside point—do not include the metal. Compare that measurement with 18.9 mm.

This is a jewellery-size conversion, not a guarantee of fit. Finger size changes with temperature and time of day; wide bands often need extra room.