If she wears rings, the easiest way to determine her size will be to borrow one she already owns. You can either trace the inside of the ring on a piece of paper, or bring the actual ring into a Ben Bridge store near you to obtain the size. A Personal Jeweler can use these measurements to identify her approximate ring size.
If you two are together in the journey of finding the perfect engagement ring, use our printable ring-sizer to measure her ring size. link http://www.benbridge.com/education/ring-sizes