Wrap a strip of paper or string around the base of the finger
Mark the point where the ends meet
Measure the length with a ruler in millimeters
Use the measured length as the ring circumference
Compare the circumference to a ring size chart
Measure the finger at the end of the day for best accuracy
Measure the exact finger where the ring will be worn
Repeat the measurement 2 to 3 times for consistency
If between sizes, choose the larger size