Find the size of the ring you need from a circumference measurement of your finger.
This type of ring sizing is used in Canada, Mexico, and the United States.
In addition to the size of the ring you need, this calculator will provide the ring's inside diameter based on your finger's circumference.
In this calculator 1 7/16" is a size 1/8 ring and on the upper end, 4 7/16" is a size 30 ring