Wrap a strip of paper or a soft measuring tape around the base of the ring finger
Mark where the ends meet
Measure the length in millimeters
Compare the measurement to a ring size chart
Measure the finger at the end of the day
Measure more than once for accuracy
Make sure the paper or tape fits snugly but not tightly
Consider the knuckle size if it is larger than the base of the finger
Use a ring that already fits and measure its inner diameter
Have a jeweler measure the finger for the most accurate result