Cut a piece of string or paper to a length of about 10 centimeters (cm).

Wrap the paper or string around your finger where you want the ring to sit. Pull so that the string fits comfortably around your finger - not too tight and not too loose.

Use a pencil to mark the point where the end of the string or paper overlaps.

Place the string or paper against a ruler or tape measure and measure the length (mm) from its end to the point you marked with the pencil. The millimeter number corresponds to the ring size.