Question: how to tell the size of your finger for a ring?
Answer: Find a piece of string or strip of paper no wider than 1.4 cm (1/2 inch).
Wrap it around the base of the appropriate finger.
Use a pen to mark the point on the string/paper where it overlaps, forming a complete circle.
With a ruler, measure the length from the starting end of the string/paper to the pen mark.