The most accurate way to determine your ring size is to visit a local jewelry store where they have several measurement tools to determine your ring size. If you have a ring that fits well and you need to find out the size, a steel ring mandrel is used. The ring is placed on the ring mandrel and the number on the mandrel that corresponds with the bottom of the ring is the ring size. Below is a picture of a ring mandrel.
Ring mandrel tool used to determine ring size. Slide ring on mandrel and read the size at the bottom of the ring.
Another jeweler’s tool used to measure ring size are metal ring sizers. This is a ring that holds all of the different ring sizes in increments that range from every quarter size to every half size, depending on the tool, so that you may try on the ring to determine which ring size fits you the best. The ring sizers come in a narrow width and a wide width to accurately determine your ring size, since a ring’s width affects the size of the ring that is most comfortable for you.
Metal ring sizers in narrow and wide width to measure ring size.