Ring sizes in the United States are measured using centimeters; your ring size is exactly equal in number to the centimeter measurement around the base of your finger.

For example, if the circumference of your finger measures 5.5cm, then your ring size is exactly 5.5. (1 inch = 2.54 cm) For imperfect sizes, consider ordering one size larger and asking your local jeweler to add a soft inner lining of gold for a truer fit.