Use this sizing table to help you find your ring size if you don’t already know it. 

We suggest using a piece of string and twisting, then trimming it at the exact length that wraps around your finger, and then measuring that length to get the circumference of your finger.

If you’re trying to buy a gift for someone else, if you can find an existing ring of theirs and measure the inside diameter, that could help you choose their size correctly.