If you're planning a proposal and don't want to tip off your partner, the good news is you have options — most jewellers will resize a ring for free if you're off by half a size in either direction. Aim for "close enough" rather than perfect, and these methods all get you there.
1 — Borrow a ring she already wears (the safest method)
If she has a ring on the same finger you'll be proposing on, this is gold. Wait until she takes it off (showering, sleeping, swimming), then either:
- Trace it. Place the ring on paper and trace the inner edge with a fine pen. Measure that diameter on our free virtual ring sizer for an exact US/UK/EU size.
- Press it into soap. Press the ring firmly into a bar of soap to make a clear imprint. Measure the imprint's inner diameter.
- Place it on the calibrated sizer. Quickest of all — put the ring directly on a calibrated screen and read the size.
2 — Ask a friend or family member
Her best friend, sister, or mum often knows. If they don't, they can find out for you in a low-key way (compliment a ring, mention rings going on sale, etc.) without raising suspicion. Sisters and mothers are especially good — they often share rings.
3 — Use a ratio from another finger
If you can measure any finger she has — even her thumb — there are common ratios:
- Index finger ≈ ring finger − 1 to 1½ sizes
- Middle finger ≈ ring finger + ½ to 1 size
- Pinky finger ≈ ring finger − 2 to 3 sizes
It's an estimate, not exact — but combined with other clues, it narrows the range dramatically.
4 — String trick while she's asleep
Wrap a thin strip of paper or string gently around her ring finger when she's deeply asleep. Mark where it meets, then measure on the calibrated ruler. Risky if she's a light sleeper — but accurate if successful.
5 — Compare hand sizes to known data
Average US women's ring size is 6 – 6.5. If her hands are smaller than average, try 5 – 5.5. If larger, try 7. Combine this with her height: petite (under 5'4") tends to size 5 – 6, average (5'4"–5'8") size 6 – 7, taller size 7+.
6 — Try a sneaky "guess" game
"I bet I can guess your shoe size. And your ring size." Most people will engage with this without realising it's a sizing recon mission. Get her to say a number out loud — and that's your answer.
7 — Buy slightly larger, then resize
When in doubt, go ½ size up. A slightly loose ring fits — a tight one doesn't even slide on. Most jewellers offer free resizing within 30 – 60 days of purchase, so this is the safest "fallback" if all else fails.
What ring size are most engagement rings?
The most common engagement ring sizes are:
- US 6 — most common for women in the US
- UK L½ – M — equivalent
- EU 52 — equivalent
If you genuinely have no clue, US 6 is the safest blind guess for a woman of average build. Then plan a resize.