Finance 6 sneaky tricks to figure out their engagement ring size, without having to ask

Many jewelers offer after-purchase resizing, for a small fee — or even for free — but if you don't get your partner's ring size right, it can put a real hitch in your perfect proposal.

The most obvious way to find out your partner's ring size? Ask them. But if you're banking on the element of surprise, you might want to be a little sneakier.

A few things to keep in mind:

• It's easier to resize a ring with a plain band than one with stones embedded all the way around, so the more stones you have, the more you'll want to get it right the first time.

• "The wider the band, the tighter the fit," notes Emily Duke of DiamondEnvy.com at The Knot. She recommends sizing up by a quarter to a half size if you're seeking a wider band.

Now, to figure out the ring size without your partner noticing, try:

1. Taking, tracing, or trying on a ring

If your partner regularly wears rings, you have a few options. When they take a ring off, you can:

• Bring it to a jeweler. Note which finger they wear it on, though — most people don't wear a ring on their left ring finger before getting engaged, so the chances this ring will be a perfect fit are slim. However, it can give your jeweler an idea of the size of their hands. If in doubt, go bigger.

• Trace it. Only have until they get out of the shower before it's gone? Grab a paper and pencil, and trace the ring. Then you can measure it using an online ring sizing guide like one from Brilliant Earth, The Knot, or Zales. Ringsizes.co has an international conversion chart that converts millimeters and inches into sizes in different countries.

• Try it on your own hand. Use a pen to mark where it fits you, or take a picture to bring to the jeweler.

• Press it into a bar of soap. It sounds a little weird, but Hamra Jewelers points out that it's an easy way to make a model of a ring to bring to your jeweler. Just make sure to wipe all the soap off before you return it!

2. Asking one of their friends

Find out her ring size without spoiling the surprise by enlisting the help of her friends or family members, suggests Jessica Anand, a jewelry expert at Brilliant Earth, an ethically sourced jeweler:

"A great way to find out her ring size is to ask one of her friends. Friends occasionally have this insight! And, if the friend doesn't know right away, she can be the one to ask (nonchalantly).

"Even better, ask the friend to take your girlfriend engagement ring shopping 'for fun.' Have her get professionally sized and ask her friend to report back to you."

3. Having them try on a friends ring

You can also get an idea of sizing by having them try on another friend's ring, Anand says:

"If one of your partner's friends is engaged, ask her friend to let your girlfriend try on the ring. This will put you in a ballpark size range to start out with.

"You can also use this as an opportunity to ask what she thought of her friend's ring (in private) and try to do a little sleuthing as to what style of ring she would like for herself."

4. Measuring their finger while they sleep

If your partner is a deep sleeper, you can wrap a piece of string or thin strip of paper around their finger and mark where it meets with a pen, suggests Wikihow. Don't use a measuring tape, cautions Today, because the tape's thickness could lead to an inaccurate reading. Then, compare the measurement to an online sizing chart like the ones noted above, or bring it straight to the jeweler. Be careful not to pull it too tight.

Tread lightly, because if they wake up, you're toast.

5. Comparing your fingers to theirs

It seems inexact, but hey: It worked for Business Insider editor Dave Smith. If you know how your partner's hand compares to yours (is your pinky about the same size as their ring finger?) you can make a decent estimate at the jeweler's. If you don't want to rely on memory, consider snapping a "romantic" photo of your intertwined hands. Just make sure to get their left.

6. Pretending youre buying a ring for someone else

Admittedly, this method is pretty transparent if you aren't the type to buy rings as gifts for your friends and family. However, if you're willing to commit to the charade, you can have your partner help you shop for a (cheaper!) ring you plan on "gifting" someone else. Have them try it on to gauge size, suggests Hamra Jewelers, and you'll know exactly what size you need. If you're really on your game, you'll call ahead to let the jeweler in on your plan.

If you're still getting nowhere, Brilliant Earth points out

The bottom line: You're making a big purchase here, so you'll want to get it right.