Without her finding out. Lol.
Most Helpful Girl
Wow….exciting time! o_O
Do NOT ask her girlfriends—they will not be able to keep the secret! Lol
Does she wear a right hand ring? You could like take it off when you’re holding her hand or w/e and try it on yourself. (on your pinkie) remember how far it will go onto your finger (mark it later) and then go to a jewler and ask to try on their ring sizer. You should be able to guess pretty accurately.
If you guys are REALLY close, you may be daring enough to check her jewelry box. (do NOT do this if there is any risk of her catching you though! Lol) find a ring of hers (that she wears on her ring finger) and check for the size that’s marked on it.
Take her bone structure into consideration. Is she skinny? Average? Large? Small or large hands? Most women wear between a size 4 and a size 9.
There is also supposed to be some kind of correlation between shoe size and ring size, but this varies quite a lot. I happen to wear a size 7 in both shoes and rings, but this is not true for everyone.
Best of Luck! I hoped this helped. Try number 1 especially!