US ring size 13

US size 13 has an inside diameter of approximately 22.2 mm and an inside circumference of 69.7 mm.

How to check whether size 13 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 22.2 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.