Whether you're buying a ring for your sister or your girlfriend, for a birthday or to propose, finding a ring that fits is essential. Rings range in size from zero to 16, plus half- and quarter-sizes. If you try to guess which one fits best, the ring will likely have to be resized later. Get the ring size right the first time around. Asking a woman directly may be the easiest way to figure out her ring size, but with a little creativity, you can find out without ruining the surprise.
Contact her mother or a friend.
Ask the person if she knows the correct ring size. If she does, that's it! You've managed to find the ring size without asking.
Ask the person if she can find out the correct ring size if she doesn't already know. Make sure she comes up with a reasonable explanation for why she's asking so that she doesn't spoil your surprise.
Locate a jewellery box belonging to the woman for whom you're choosing a ring.
Find a ring. Make sure it's one that she has worn recently, and that it's one she wears on the correct finger.
Borrow the ring.
Have the ring sized by a jeweller.
Don't forget to return the ring---you don't want to tip her off.
Ask her if you can wear one of her rings, either around your neck on a chain or on your pinky finger.
Select a ring that she wears often, but make sure she sports it on the correct finger. Choosing a ring that she wears on her index finger won't help you size a ring for her ring finger.
Take the ring to a jeweller and have it sized.
Print a free online ring sizer.
Measure the ring sizer with a ruler to check its accuracy.
Wait until she's asleep. Alternately, if you know someone who is of a similar size to the woman you're buying a ring for, you can ask to measure her finger instead. Keep in mind that with this method, you might not get an accurate result.
Place the ring sizer around her finger.
Pull the ring sizer until it is snug. This will provide the most accurate size information.
If you decide to ask her mother or friend for the ring size, warn them to be discreet. Make sure they know not to drop any hints that will ruin the surprise. If you choose to borrow one of her rings for sizing, be sure to put it back before she discovers that it's missing. If she does discover that one of her rings is missing, try leaving the ring in a location where she might plausibly have lost it, such as beneath her jewellery box.