www.stores.ebay.com/gewelometrySelling rings you come across a common question.
How do I know what size my finger is for the ring I wish to buy???
One suggestion would be to go to your local jeweler,
and he could size your finger for you.
Second method, you could try in the comfort of your home:
Take a piece of wire and twist it around your finger.
Cut at twist and straighten the wire out.
Measure from twist to end.
That measurement (inches or centimeters) will translate into
your finger size.