Measure the inner diameter of your own ring with great precision to make sure you have the number you need. B.C. inner diameter 1,7ector = 17mm ring size.
Take a thread or a strip of paper or a tape measure.
Wrap it around your finger (not too tight) to create a circle around it.
Mark the point that meets its end
Measure in millimeters the length from the edge to the point you noted. This is the inner perimeter. Please refer to the table below for pairing. If e.g. you measured 53,1mm then the ring you make is 17.
Usually your "good" hand, what you use most for jobs, tends to be a bit bigger and the fingers a little swollen.
If the measurement is between 2 numbers, you prefer the larger ring.
Fingers can swell during the day or hotter days.
1cm = 10mm (1 cm corresponds to 10 mm). E.g. 5,3cm = 53mm