How to buy an engagement ring
Figuring out ring size
Don't know the ring size, but still want to make the engagement a surprise? Don't fret, there are a couple of ways to find out without raising her suspicions.
De Beers Jewellery recommends these tricks: Make an impression of another ring in between two bars of soap, trace the inside of a ring on a piece of paper, try a ring on for size and see how far down your finger it goes, enlist a friend to ask the question, or, best of all, bring one of her rings with you.
Or, you could just call MacGyver.