The best way to find out the size of the ring is to
measure the circumference of the ring using paper. Cut out a piece of paper
(measuring strip) with a width of 15 mm and a length about 80 mm (it is
possible to use a thread also). Then wrap the measuring strip around your
finger (measuring strip needs to be wrapped tightly around your finger, but not
too tightly, and then mark the place with a pen or a marker where the paper mingles
with the beginning of the paper. Attach the paper to the ruler and measure from
the beginning of the paper to the place you have marked. The paper length in mm
corresponds to the size of the ring. i.e. if paper length (1. circumference) is
50 mm your ring size is EU 10 or 50.

Another way to find out your ring size if you already
have a ring - you can measure the diameter of the ring and look up for your
size at table above (2. Diameter), i.e. if your ring diameter is 15.90 mm your
ring size is EU 10 or 50.