Wrap a strip of paper, string, or floss around the base of the finger
Mark where the ends meet
Measure the length in millimeters with a ruler
Compare the measurement to a ring size chart
Measure the same finger at the end of the day
Measure more than once for accuracy
Make sure the strip is snug but not tight
If the knuckle is larger, measure both the knuckle and the base of the finger
Use a ring that already fits and measure its inside diameter
Compare the inside diameter to a ring size chart
Check the size in warm conditions if your fingers swell easily
Avoid measuring when your fingers are very cold
If between sizes, choose the larger size
Confirm the size using a printable ring sizer if available