To measure a person's ring size with a piece of paper, cut a thin strip of paper and tape one edge of the paper to the knuckle of the person's ring finger. Wrap the strip around the finger, mark the spot that meets the edge and measure the distance. The exact measurement of a size five ring is 1 15/16 inches. There is a difference of 1/8 inch between sizes.
After measuring the person's ring size with a strip of paper, cut the paper at the mark and tape the edges together to create a test ring. If the paper ring feels tight, particularly when sliding over the knuckle, the person needs a ring one size larger. Unlike paper, a ring doesn't stretch.
Other methods of determining ring size include using a piece of string or an existing ring. The string method is performed the same way as the paper method. To use an existing ring, place the ring on a ring size chart. Ring size charts are available from jewelers and on certain jeweler's websites, such as TungstenOvernight.com.
When a person is cold, her fingers shrink. Take measurements in warm conditions. Measure the finger multiple times for accuracy.