Finding her ring size without asking

You want it to be a surprise, which rules out the one easy method. Here is what works, in order, and what to do when none of it is possible.

Published 2026-10-23

The honest first point: you do not need to be exactly right. Most engagement rings — a solitaire on a plain shank — size up or down two sizes for a modest fee, and many jewellers include the first resize free. Getting within a size is a success. Getting the proposal right matters more.

The second honest point: the average is a weak guess. Jewellers stock women's rings from about US 5 to 7 and sell US 6 most often, but that range covers 5.1 mm of circumference. Picking the middle gives you roughly a one-in-four chance.

1. Borrow a ring she already wears

By a long way the best method, and the only one that gives you a real measurement. Take a ring from a jewellery box — not off her hand — and note which finger and which hand she wears it on, because that is half the information.

Then do one of these:

• Lay it on the circle chart on screen after calibrating with a bank card. Takes a minute, accurate to about a quarter size.
• Print the circle sheet and put the ring on the circles. Check the 50 mm line first with a ruler.
• Measure straight across the inside with a ruler, at the widest point. Measure the hole, not the metal.
• Press it into soap or modelling clay and measure the impression — only if you cannot keep the ring for two minutes.

If the borrowed ring is from the right hand and the engagement ring goes on the left, take off a quarter to a half size: the dominant hand is usually slightly larger.

One caution with borrowed rings: fashion rings bought online are often sized loosely, and stacking rings are made to sit lower on the finger. A ring she wears every day — an old family ring, or one she was measured for in a shop — tells you far more than one she wears now and then.

2. Have someone else ask

Her mother, her sister, her closest friend. They can ask a direct question that would give you away instantly, and most people happily know their own size. The risk is not accuracy, it is discretion — pick the one person who can keep it.

A variation that works: ask the friend to go ring shopping "for themselves" and get both of them sized in a shop. The size is then taken on a steel mandrel, which beats everything else on this list.

3. Draw round the inside of a ring

If you cannot take the ring out of the house, put it on a piece of paper and trace the inside circle carefully with a sharp pencil held upright. Then measure across your drawing. It is cruder than the other options — the pencil adds a little — but it gets you within about a size, and the ring never leaves the room.

4. The string-on-her-finger trick (when she is asleep)

It is in every list of this kind and it mostly does not work. Fingers at rest are at their smallest, the thread will wake a light sleeper, and you cannot wrap snugly without pulling. If you try it, treat the answer as a lower bound and add half a size.

5. Guess from the hand

A rough guide, worth something only if you have nothing else:

A guide to what shops stock, not a measurement. Use it only as a tie-breaker.

Height and build predict finger size better than anything else you can observe, but the error is still more than a size. Someone who climbs, gardens or works with their hands runs larger than their build suggests.

6. Buy a stand-in ring

Propose with a plain inexpensive band, a family ring, or even a ribbon, and choose the real ring together afterwards. This is increasingly common and it solves two problems at once: the size, and whether she likes the ring at all.

If the design must be a surprise but the size need not be, the reverse also works: buy the ring you chose, in a size you are confident is too large, and book the resize for the week after.

7. Order large on purpose

If you are down to a coin flip, order the larger. A ring that is too big can be worn on the proposal day — on another finger if need be — and sized down cleanly. A ring that is too small cannot go on at all, which is the one outcome you really want to avoid in that moment.

Check your answer

Whatever you end up with, put the number into the converter and look at it in millimetres. If the circumference is far outside the usual stocked range, something has gone wrong — most likely the ring you measured was from a different finger, or you measured the outside of the band.

Before you buy

1. Confirm the ring can be resized at all — ask specifically about eternity bands and tension settings, which cannot.
2. Ask whether the first resize is free and for how long. Many jewellers offer twelve months.
3. Ask what the return policy is if she wants a different ring entirely.
4. Keep the receipt somewhere she will not find it.

And if you want the context behind the numbers, average ring size sets out what the stocking ranges do and do not tell you.