Measuring a girl's ring finger without her knowing allows you to surprise her with an engagement ring or a ring for a special occasion. There are several ways to find out someone's ring size secretly, so you can keep the romance and excitement of the occasion alive. Since most jewellers will not take back or exchange rings that have been sized, make sure your measurements are exact.
Sneak a ring that the girl wears on her ring finger to a jeweller to have it sized. If you do not think you can get away with borrowing a ring for a day, print a ring size chart from a trusted jeweller's website or purchase a ring-sizer stick. Use the chart or stick to measure a ring that the girl wears on her ring finger.
Slip a ring that the girl wears onto one of your fingers and mark where the bottom of the ring rests on your finger with a permanent marker. Using a permanent marker will ensure that the mark does not rub or wash off before you get to a jeweller.
Make an impression in putty of a ring she wears on her ring finger and take it to a jeweller for measuring.
Ask her best friend, mother or sister for her ring-finger size. It is likely that a close female friend or relative will know, as women often share jewellery or shop together.