Ring Size in Secret: 7 Ways to Find It Out Before the Proposal

To find out her ring size in secret, the most reliable method is to borrow a ring she wears on her ring finger for five minutes and measure its inside diameter: 16.6 mm across corresponds to a French size 52. And if you have no clue at all, don’t worry: at Laveran, resizing is free for life, on engagement rings from €880. Here are the 7 discreet methods we recommend before a proposal, from the most accurate to the most approximate, with their pitfalls.

Contents

• How can you find out her ring size in secret?
• Method 1: measure a ring she already wears
• How can you find a ring size without a ring sizer?
• Can you measure her finger while she sleeps?
• Who can help you find her size?
• No clue at all: which ring size should you choose?
• Which ring should you choose if you’re unsure of the size?
• What if the ring doesn’t fit on the big day?
• FAQ

How can you find out her ring size in secret?

There are 7 ways to find out your girlfriend’s ring size without her knowing, and the best one depends on a single question: does she already wear a ring? If she does, you can get an almost exact measurement. If not, you will need help from someone close to her, or an estimate. Here is how they compare:

One thing matters most: the borrowed ring must be worn on the ring finger, ideally on the hand where she will wear the engagement ring (in France, the left ring finger). A ring worn on the middle finger or on the right hand gives you an indication, not a measurement.

Method 1: how do you measure a ring she already wears?

Measure the inside diameter of the ring in millimeters, then multiply it by 3.14: the result is her French ring size. In France, a ring size is simply the circumference of the finger in millimeters. A ring with an inside diameter of 16.6 mm is therefore a size 52.

For an accurate measurement:

• measure inside the band, from one inner edge to the other, through the center;
• use a ruler marked in millimeters, or better, a caliper;
• note the result to a tenth of a millimeter: a 0.3 mm difference already equals about one size;
• avoid very wide or misshapen rings, which skew the result.

Need the US or UK equivalent? Our ring size conversion chart gives every conversion.

How can you find a ring size without a ring sizer?

Without a ring sizer, the simplest approach is to copy the inside of her ring: a tracing on paper, an imprint in soap, or a mark on your own finger. Each of these takes a minute, which makes them ideal when you only have the ring for a short time.

Method 2: trace the inside of the ring

Lay the ring flat on a white sheet and trace the inner outline with a very sharp pencil held straight up. Then measure the diameter of the circle, or simply bring the sheet to a showroom: we find the size in a few seconds.

Method 3: an imprint in soap

Press the ring flat into a bar of soap, then lift it out carefully. The imprint keeps the inside diameter, which you can measure later at your leisure. Remember to rinse and dry the ring before putting it back.

Method 4: the ring on your own finger

Slide her ring onto one of your fingers, often your little finger, and mark with a pen where it stops. Then measure your finger at that spot with a ring sizer. It is discreet but less accurate: allow for a margin of error of about one size.

The ring sizer itself costs nothing: you can download our printable ring sizer or request the free ring sizer. All the other measuring techniques are covered in our guide how to measure your ring size.

Got a tracing, an imprint or one of her rings? Bring it to one of our 11 showrooms or show it on a video call: an expert finds her size with a professional ring sizer, then helps you choose the ring. Certified lab-grown diamonds, from €880. Book an appointment →

Can you measure her finger while she sleeps?

It is possible, but it is the least reliable method: a string or strip of paper is often off by one or two sizes. If you try it, wrap a thin string around the base of her ring finger without pulling it tight, mark with a marker where the two ends meet, then measure the length laid flat. The result in millimeters is the French size.

Three limits to keep in mind:

• string stretches and paper folds, which distorts the measurement;
• finger size changes during the day and with temperature: fingers are slimmer in the cold and more swollen in the evening or in summer;
• a ring has to slide over the knuckle: if her knuckles are prominent, add half a size.

Treat the result as an indication, and cross-check it with another method if you can.

Who can help you find your girlfriend’s ring size?

A sister, a close friend or her mother may already know her ring size, and can find it out without raising suspicion. It is often the easiest method when she doesn’t wear rings.

• Ask them directly: some have already given her a ring or gone shopping with her.
• The shopping excuse: a friend takes her to try on rings “just for fun” and notes the size that fits.
• The ring swap: a friend borrows one of her rings for an evening and lends it to you long enough to measure it.

Choose someone who can keep a secret, and don’t put them in an awkward spot if they would rather stay out of it. For choosing the design itself, read our guide proposal ring: choosing well without knowing her taste.

No clue at all: which ring size should you choose?

If you really have nothing to go on, choose a middle size and have the ring adjusted after the proposal: at Laveran, resizing is free for life. This is the seventh method, and it has one advantage: the surprise stays complete.

A few pointers to get as close as possible:

• compare with your own hands: if her fingers are clearly slimmer than yours, go one or two sizes below your ring finger;
• if you know her middle-finger size, subtract about half a size to one size for the ring finger;
• if you are torn between two sizes, take the larger one: a slightly loose ring can be worn until it is adjusted, while a ring that is too small won’t go over the knuckle.

Many couples actually propose with a ring “to be adjusted” and then visit a showroom together for the final sizing. It becomes part of the moment.

Which ring should you choose if you’re unsure of the size?

A solitaire on a plain band is the easiest to resize. The band holds no stones, so adjusting it is straightforward work. A diamond pavé band can be adjusted too, but it is a more technical design. Here are the actual prices of our most requested engagement rings, with H/VS2 lab-grown diamonds, as of October 2026:

These prices are the same in 18k white, yellow or rose gold and in platinum 950: platinum costs the same as gold. All our lab-grown diamonds are certified by IGI or GIA, with no fluorescence. A lab-grown diamond is pure carbon, with a hardness of 10 and the same sparkle as a natural diamond, and costs up to 80% less than a natural diamond of equivalent quality. Installment payments are available with Alma, and engraving is free.

The whole collection: lab-grown diamond engagement rings.

What if the ring doesn’t fit on the big day?

It is never a problem: every Laveran ring can be resized free of charge, for life. After the proposal, you visit one of our showrooms together for the final sizing. Every ring also comes with:

• free resizing for life;
• returns accepted within 30 days;
• a lifetime warranty;
• free polishing and prong checks for life;
• free, insured, hand-delivered shipping.

As for timing, each ring is made to order in 2 to 3 weeks. Some designs are in stock, and some can be made in a few days with express production: the exact lead time is confirmed at your appointment. For a Christmas proposal, order before the end of November, as explained in our article Christmas proposal: when to order the ring.

FAQ

How can I find out my girlfriend’s ring size without her knowing?

Borrow a ring she wears on her ring finger and measure its inside diameter, or trace its outline on a sheet of paper. With no ring to borrow, ask a friend or her sister, or choose a middle size: resizing is free for life at Laveran.

How do I convert a ring’s diameter into a size?

Multiply the inside diameter in millimeters by 3.14. The result is the finger circumference, which is also the French size: 16.6 mm across gives a size 52, 17.2 mm a size 54.

How can I find a ring size without a ring sizer?

Measure the diameter of a ring that fits, or wrap a thin string around the finger and measure the length laid flat. The string is less accurate. You can also download our free printable ring sizer.

What if I get the size wrong?

Nothing serious: at Laveran, resizing is free for life, including after the proposal. You can also return the ring within 30 days.

Is it better to have a ring that is too big or too small?

Slightly too big. It can be worn until it is adjusted, whereas a ring that is too small won’t go over the knuckle on the day of the proposal.

Is the Laveran ring sizer really free?

Yes. You can download the printable ring sizer or request it free of charge. In a showroom, an expert measures the finger with a professional ring sizer.

Should you measure the left or right ring finger?

The one where she will wear the engagement ring, which in France is the left ring finger. Both hands are not always the same size, especially the dominant hand.

How much does a lab-grown diamond engagement ring cost?

At Laveran, engagement rings start at €880 (0.30 carat, H/VS2 quality), and a 1-carat solitaire costs €1,744, with an IGI or GIA certificate.

Found her size, or at least a clue? The hardest part is done. Book an appointment in one of our 11 showrooms in Paris, Lyon, Nice, Marseille, Bordeaux, Toulouse, Lille, Montpellier, Annecy, Aix-en-Provence or La Rochelle, or by video call: we check the size with you and help you choose the ring that suits her.

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