Measuring a Ring You Already Own
Place the ring on a ruler or caliper.
Measure the inside diameter of the ring (from inner edge to inner edge, in millimeters, without including the thickness of the band).
Measuring Your Finger with a String or Measuring Tape
Cut a thin strip of paper, use a flexible measuring tape, or use a piece of string.
Wrap it around the base of your finger without pulling it too tightly.
Mark the point where the strip or string meets.
Measure the length with a ruler in millimeters. This is the circumference of your finger.
