You want to buy her a ring. You do not know her ring size. And you cannot ask without giving the game away. The internet is full of tricks for this. String around the finger while she sleeps. A ring borrowed from her jewellery box. Modelling soap. Some of them work. Others will hand you a measurement that is two sizes out. And there is one option almost nobody mentions, which is often the right one.

The only reliable method: borrow a ring

Take a ring she already wears. Measure its inside diameter. That is all.

Three precautions, and they matter more than the measurement itself.

Take a ring from the right finger. A ring finger and a middle finger often differ by one or two sizes. A ring worn on the little finger tells you nothing about the ring finger. If you do not know which finger the borrowed ring came from, the measurement is worthless.

Measure the inside diameter, not the outside. Lay the ring on a ruler marked in millimetres. Read the inside distance from edge to edge, at the widest point. Multiply by 3.14 to get the inside circumference. Most European systems, including the French one, express size as that circumference in millimetres minus 40, so a 54 mm circumference is a size 54. UK and US sizing use entirely different scales, so convert rather than guess.

Put the ring back where you found it. That sounds obvious. Plenty of proposals have been given away by a ring found on the bedside table.

If you would rather not borrow anything, our guide to finding your ring size goes through the measuring methods and their pitfalls.

The tricks that circulate, and what they are worth

Let us go through them honestly.

String or thread around the finger. It works badly. The thread stretches, or it squeezes the skin. The typical error is one size, sometimes two. If it is all you have, measure three times and keep the largest value.

A strip of paper. Better than string, because paper does not stretch. But you have to pass the strip over the knuckle, and it is the knuckle that decides, not the base of the finger.

Asking her best friend or her mother. An excellent method, if the person can keep a secret. Often they already know. More often still, they have an identical ring and can measure it.

Comparing against your own finger. Slide one of her rings onto one of your fingers and note how far it goes down. Then measure your own finger at leisure. A homespun method, but it beats string.

Making a soap impression. Forget it. The paste deforms, the reading is approximate, and you lose an evening.

One point nobody mentions: fingers change size through the day. They swell in the evening, they swell in hot weather, they swell after exercise and after a salty meal. The gap can reach half a size. Measure late in the day, at normal temperature. You will avoid the ring that slides on in the morning and jams by evening.

The margin of error you can live with, and the one you cannot

Not all errors are equal.

Half a size too big. Comfortable. The ring turns a little, but it can still be worn. A jeweller tightens it easily.

A full size too big. Annoying but fixable. The ring turns properly and the stone tips underneath the finger. A trip to the workshop is advisable.

Too small, by any margin. This is the bad side of the error. A ring that is too small cannot be worn at all, whereas a ring that is too big can be worn while you wait. And enlarging a band stretches the metal, which thins it at the solder.

The rule to remember: when in doubt, go up a size. Erring on the large side is always less serious.

The rings that cannot be resized

Here is the point guides leave out systematically, and it is the one that costs the most.

Not every ring can be resized. Some cannot be resized at all.

The full eternity band. The stones go all the way round. There is no free metal to cut. You do not resize it, you remake it.

Rings with a continuous pattern. An engraved decoration or a relief running round gets cut cleanly in two by the solder. Technically possible, visually ruined.

Rings with stones on the shoulders. When the stones run far down the sides, the free zone becomes too short. One size is possible, rarely more.

Rings in metals that cannot be worked hot. Titanium, tungsten, ceramic. A jeweller will not resize them. At Lauredi the question does not arise: we work only recycled 18 carat gold, rhodium plated 925 silver and vermeil, and all three can be reworked.

The practical conclusion. If you are buying while guessing the size, choose a ring with a plain band and one or three stones grouped on top. You keep room to manoeuvre. An eternity band bought blind is a bet you have already lost.

The option nobody suggests: do not buy a ring

No jewellery guide writes this sentence, because no jeweller wants to steer you away from a ring. We are going to write it anyway.

If you do not know her size, and you have no reliable way to find it out, give something else. A necklace, earrings, a bracelet. Then choose the ring together.

Three reasons.

Taste matters as much as size. A ring is worn every day for years. The shape of the stone, the height of the setting, the width of the band: these are deeply personal preferences. Guessing the size is a mechanical problem. Guessing the taste is a much harder one.

The surprise survives intact. A necklace given in a beautiful box has exactly the same effect on the day. The proposal keeps its moment. Choosing the ring becomes a second moment, shared.

You skip the workshop. No resizing, no delay, no piece of jewellery sitting in a drawer for three weeks.

This is a real and growing trend. More and more couples buy the ring together after the proposal. There is nothing less romantic about it. There are simply two people wearing a piece they chose.

If the ring is too big or too small on the day

It happens. It is not serious. Here is what to do.

Do not force it. A ring that is too small sometimes goes on if you force it. It does not come off. The finger swells, and the situation turns medical.

Do not improvise a permanent fix. Plastic ring reducers will get you through an evening. Worn continuously, they trap moisture against the metal and against the skin.

Allow for the real lead time. Resizing at a jeweller generally takes one to two weeks. The band has to be cut, soldered, reshaped, repolished, and the setting checked. It is handwork.

Know that a band cannot be reworked forever. Every resizing works the metal. Two or three times in the life of a ring is reasonable. Ten is not.

After a trip to the workshop, always check the setting before wearing the ring again. Our care guide explains the ten second check that stops you losing a stone.

Ordering online without getting it wrong

Three reflexes before you confirm the basket.

Check the returns and size exchange policy. It should be written in black and white, with a clear deadline. In France, where we ship from, buyers have fourteen days to withdraw from an online purchase, except on personalised or bespoke pieces. Your own country's rules may differ, so read the terms that apply to you.

Check whether the house offers a resizing service, and on what terms. That is the service that makes the difference when you are buying blind.

Finally, order early. Making time plus any resizing time quickly adds up to a month. For end of year proposals, starting in November is not excessive.

If you are torn between several pieces, browse our rings in recycled 18 carat gold. And if the project calls for a unique piece, our bespoke service starts from your idea. If the doubt is about the moment rather than the size, our article on promise, engagement, wedding and eternity rings helps you place the right ring.

What to take away

Borrowing a ring from the right finger is still the only reliable method. Everything else is an approximation, and approximation is paid for in workshop visits.

When in doubt, go up a size, and choose a plain band model that can be reworked. Avoid an eternity band until the size is certain.

And if you genuinely have no lead at all, give a necklace, a bracelet or earrings. Then go and choose the ring together. It is the answer few jewellers give, and it is often the best one.

FAQ

How do you find out someone's ring size without asking?

Quietly borrow a ring she wears on her ring finger and measure its inside diameter in millimetres. Multiply by 3.14 for the circumference, then convert to your local sizing scale. It is by far the most reliable method, well ahead of string.

What is the most common women's ring size?

Around a 52 to 54 European size on the left ring finger, which is roughly a UK L to N or a US 6 to 7. That is only an average. It does not excuse you from measuring, and betting on an average is still a bet.

Should you go bigger or smaller when in doubt?

Bigger, always. A ring that is too large can be worn while it waits for adjustment and is easy to tighten. A ring that is too small cannot be worn at all, and enlarging it stretches the metal.

Can every ring be resized?

No. A full eternity band set all the way round cannot be resized. Rings with a continuous pattern and rings with stones running down the shoulders offer very little margin. Check this before buying, not after.

How long does resizing a ring take?

Allow one to two weeks at a jeweller. The band has to be cut, soldered, reshaped, repolished and the setting checked. If the piece is for a specific date, add that time to your planning.

Can you propose with a ring and change the size afterwards?

Yes, it is common, provided you chose a resizable model. Plenty of couples have the ring adjusted in the weeks after the proposal, and it takes nothing away from the moment.

What should you give when you really do not know the size?

A necklace, earrings or a bracelet. Those three need no measurement and can be worn immediately. The ring is then chosen together, and you can be certain she will like it.

Fiona