THE FIT FORMULA
The way a ring fits and feels mostly depends on the size of your finger, the shape of your knuckles, and the style of the ring.
For a more visual approach, do the following:
Cut a piece of string or a thin strip of paper and wrap it around the base of your finger.
Mark the point where the ends meet.
Use a ruler to measure the length of the string or paper in millimeters.
Compare the measurement to a ring size chart to find your corresponding ring size.