Visit a jeweler: The easiest and most accurate way to determine your ring size is to visit a jewelry store and have your finger measured by a professional. Use a ring sizer: If you can't visit a jeweler, you can order a plastic or metal ring sizer online or from a jewelry supply store. This will give you a more accurate measurement than using a paper or string method. Measure an existing ring: If you have a ring that fits comfortably on the finger you'd like to wear your new ring on, you can use it as a guide. Measure the inside diameter of the ring or trace it onto a piece of paper, and then use a ruler to measure the diameter. String or paper method: If you don't have an existing ring or a ring sizer, you can wrap a strip of paper or string around the base of your finger and measure the length. Then use a ruler to measure the length of the paper or string and compare it to a ring size chart to determine your ring size.