Most jewelry stores have a series of test rings that they will put on your finger to determine your ring size. You can determine your ring size at home, though, using a string and a ring sizing chart. The string should not be very elastic or it will be hard to determine the exact circumference of your finger. Using string to measure your ring size can be particularly useful if you are purchasing jewelry online and cannot try on the rings before you make your purchases.
Select a length of string at least 3-inches long. The string should not be more than 3/4-inches wide and should not stretch.
Wrap the string around your finger where you would wear your ring. The string should be tight enough to prevent it from slipping off but not so tight that it is uncomfortable.
Mark the string where it completes one circle around your finger.
Measure the length of the string needed to encircle your finger.
Determine your ring size by converting the number of inches to a ring size chart. For example, if the circumference of your finger equals 1.84 inches, you would wear a size 4 ring.