Use a ring sizer tool or ring size chart
Wrap a strip of paper or string around the base of your ring finger
Mark where the ends meet
Measure the length with a ruler in millimeters
Compare the measurement to a ring size chart
Measure your finger at the end of the day
Measure when your hands are warm
Measure the exact finger you will wear the ring on
Repeat the measurement 2 to 3 times for accuracy
If between sizes, choose the larger size