Using the Inner Diameter of Your Ring
Step 1: To find out your ring size, take a ruler and measure it with the largest inner diameter of your ring.
Step 2: Using the table below, match the diameter of the ring to your ring size. If your ring size is in between sizes, choose the one nearer to your measurement. For example, if the inner diameter of the ring is 1.6cm, it is between size US 5 and US 5.5. Since 1.6cm is closer to 1.61cm, pick US 5.5.