To measure your ring size:
Measure your finger: Wrap a tape measure around your finger making sure it is snug but not too tight. If you don't have a tape measure, you can use a piece of string and then measure the string with a ruler.
Wrap string or paper around the base of your finger. Mark the point where the ends meet with a pen.
Measure the string or paper with a ruler (mm) then divide by 3.14 (or Pi) to get the diameter of the ring.
Use the measurement to find your corresponding size in the chart. If your rings measurements fall between two sizes, it's usually best to go with the larger size.