subject: Advice On Buying A Diamond Engagement Ring [print this page] Picking out the ideal ring for your girlfriend is not your only concern. You are also going to have to find out her ring size. To do this, you will need to get a hold of a ring she currently wears on the ring finger of her left hand and determine its size. Another way to get her size is to take one of her gloves to the store with you. Another suggestion is to draw around her hand, pretending you are just doing it for fun.