How to Find Out Their Ring Size Without Asking — or Measuring
Planning a surprise? How to learn their ring size without asking: the borrowed-ring trick done right, who to ask, a safe guess, and a ring that forgives a wrong one.
You can learn someone's ring size without asking and without measuring their finger. The most reliable way is to borrow a ring they already wear on their ring finger and have it measured. A jeweler can size it quickly, and you can get close at home too. The catch is that the wrong ring can put you off by a size or more, so it's worth knowing which ring to borrow.
If you'd rather measure your own finger, that's a different job, and a ring sizer or a jeweler is the way to do it.
Borrow a ring they already wear
Look for a ring your partner often wears on the ring finger, ideally a plain band. Slip it out when they won't miss it for an hour or so, and do one of these:
- Take it to a jeweler. They'll slide it onto a ring mandrel, a tapered rod marked with sizes, and read off the size, down to a half size.
- Press it into a bar of soap. Push the ring into the soap to leave a clean impression, wipe the ring before you put it back, and take the soap to a jeweler.
- Trace the inside on paper. Draw around the inside edge with a sharp pencil, then measure across the circle.
- Measure the inside yourself. Lay a ruler across the inside of the ring, from inside edge to inside edge at the widest point, and read it in millimeters.
Then match your measurement to a size:
| US size | Inside diameter | US size | Inside diameter |
|---|---|---|---|
| 4 | 14.9 mm | 8 | 18.1 mm |
| 4½ | 15.3 mm | 8½ | 18.5 mm |
| 5 | 15.7 mm | 9 | 19.0 mm |
| 5½ | 16.1 mm | 9½ | 19.4 mm |
| 6 | 16.5 mm | 10 | 19.8 mm |
| 6½ | 16.9 mm | 10½ | 20.2 mm |
| 7 | 17.3 mm | 11 | 20.6 mm |
| 7½ | 17.7 mm | 11½ | 21.0 mm |
Each half size is only about 0.4 mm wider than the one before, so a ruler at home gets you within about half a size. A jeweler's mandrel is exact, which is why it's worth the trip.
Check which ring you borrowed
A borrowed ring only tells you the size of the finger it came from. Before you trust it, check four things:
- The finger. A ring worn on the middle finger, index finger or thumb won't be the same size as the ring finger. Only borrow one from the ring finger.
- The hand. For a right-handed person, the left ring finger is usually about half a size smaller than the right, and the other way round for left-handers. A ring from their right hand may be half a size too big for an engagement ring worn on the left.
- The band width. Wide bands fit more snugly than thin ones, so they're usually made a little larger. If you borrowed a wide band and you're buying a slim one, or the other way round, tell the jeweler.
- The season. Fingers swell in the heat and shrink in the cold. A ring that fits them in winter can feel tight in summer.
Whichever method you use, tell the jeweler which hand and finger the ring comes from and which hand your partner writes with. Our guide to which hand a wedding ring goes on covers the hand question in more detail.
Other ways to find out quietly
- Ask a friend or family member. A best friend, sister or parent may know the size, or may know a ring that fits. Some people bring one of them along to the jeweler.
- Buy a costume ring "just for fun". If a cheap ring they try on while you're out together fits their ring finger, buy it. Now you have a ring to measure.
- Skip the string. Wrapping string or paper around a finger stretches, curls and ignores the knuckle, which is often wider than the base of the finger. It's also hard to do without giving the game away.
If you have to guess
Jewelers often say women's ring sizes cluster around 6 to 7 and men's around 9 to 10. Treat that as a starting point only: it's an average of rings sold, not a measurement of anyone's finger, and plenty of people fall outside it.
If you're torn between two sizes, go up rather than down. A jeweler can take metal out of a ring that's too big more easily than they can add metal to one that's too small, and a ring that's only slightly loose can be snugged up with small metal beads fitted inside the band.
Pick a ring that forgives a wrong size
Some designs are easy to resize and some aren't, because resizing means cutting and reshaping the band. The more of the band is covered in diamonds, the harder that gets.
| Design | Resizing | Why |
|---|---|---|
| A solitaire or other design on a plain metal band | Usually easy | There's plain metal to cut and reshape |
| A plain wedding band | Usually easy | It's all metal |
| Pavé band | Hard | Reshaping the band can loosen the small diamonds set across it |
| Channel-set band | Hard | The diamonds sit in a groove that runs along the band |
| Full eternity band | Very hard | Diamonds go all the way around, so there's no plain metal to work with |
| Twisted, split or multi-row band | Harder | There's more than one band to rework |
So if you're guessing, a solitaire engagement ring on a plain band is the safest choice, and a full eternity band is the riskiest.
With us, eligible rings get one free resize within 30 days of delivery. Some designs can't be resized, or only within a limited range, so ask us before you order if you're unsure. Resized pieces are final sale, so it pays to get the size as close as you can before the ring ships. See our lab grown diamond engagement rings to start looking.
