To find the right size of the ring you desire to buy :
1) Print this document A4 and be careful that you have not selected the printing option “fit to page” ;
2) Verify, with a ruler, that the below scale is right (exactly 10 centimeter )
3) Put one of your rings, that you already own, on the circles and find the right size : the one where the printed circle is hardly visible in the inside of your ring.

PDF Rings sizes