How to Find Her Ring Size Without Asking

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If the proposal is a surprise, you cannot ask. Here are five reliable ways to find her ring size without giving the game away, ordered from most to least stealthy — plus a conversion chart, the reasons a finger changes size during the day, and what to do if you get it slightly wrong.

Key takeaways

• The most reliable method is to borrow a ring she already wears on that finger.
• The string or floss method works if you cannot borrow one.
• Most women's ring sizes fall between US 5.5 and 7, with 6 to 6.5 the most common.
• Fingers change size through the day — measure in the evening at normal temperature, never on a cold morning.
• A wider band fits tighter, so band width changes the answer.
• If you are unsure, size up slightly — a loose ring is the easier fix.
• Every Montare ring includes a free resizing in the first 60 days.

1. Borrow a ring she already wears (most reliable)

Take a ring she wears on the same finger — typically the fourth finger of the left hand. Bring it to a jeweller, or trace its inner circumference on paper and measure the inside diameter in millimetres at the widest point. Even a ring from a different finger gives a useful calibration: rings from the right hand usually run about a half size larger, since the dominant hand tends to be slightly bigger.

Two cautions. Choose a ring she wears regularly rather than one sitting unworn in a drawer — that one may be in the drawer precisely because it no longer fits. And return it before it is missed; a favourite ring going astray during the run-up to a proposal has ended more than one surprise.

2. The string method

While she is asleep, gently wrap string, floss or a strip of paper around the base of her ring finger and mark where the ends meet. Measure that length in millimetres — that is her finger circumference — and convert using the chart below. Wrap it snugly rather than tightly, and remember the ring must also pass over the knuckle, which is usually the wider point.

3. Trace a print

Press one of her rings flat into a soft surface — a pad of paper, foam, even a bar of soap. The indent shows the inner diameter; measure straight across the circle in millimetres. Less precise than taking the ring to a jeweller, but it leaves the ring exactly where it was found.

4. Recruit a friend

Her sister, best friend or mother. Ask one of them to take her shopping for a non-engagement piece and quietly get her size measured, or simply to try on rings together. The most reliable version of this is the friend who can ask directly under cover of an unrelated conversation — people share their ring size readily when nothing appears to be at stake.

5. Order a Montare ring sizer (best fallback)

We send a free plastic ring-sizer kit anywhere in Canada. Try it on your own finger first to learn how the scale reads, then find an excuse for her to try one on. Order one from our ring sizer page.

Millimetres to ring size

Whatever method you use, you will end up with a measurement in millimetres. Inside diameter and circumference are the two universal figures — every national sizing system is derived from them.

US size	Inside diameter	Inside circumference
4	14.9 mm	46.8 mm
4.5	15.3 mm	48.0 mm
5	15.7 mm	49.3 mm
5.5	16.1 mm	50.6 mm
6	16.5 mm	51.9 mm
6.5	16.9 mm	53.1 mm
7	17.3 mm	54.4 mm
7.5	17.7 mm	55.7 mm
8	18.1 mm	57.0 mm

If you have a circumference and want the diameter, divide by 3.14. Half sizes are roughly 0.4mm of diameter apart, which is why a careful measurement matters — a 1mm error is more than a full size.

Which method to use

Method	Stealth	Reliability
Borrow a ring	High	High
String / floss	High	Medium
Trace a print	High	Medium
Recruit a friend	Medium	High
Montare ring sizer	Medium	High

Fingers change size — measure at the right moment

No finger has a single fixed size, which is the main reason otherwise careful measurements go wrong. Fingers are at their smallest in the cold and first thing in the morning, and at their largest in heat, late in the day, after exercise, after salty food or alcohol, and during pregnancy. The swing between a cold morning and a warm evening can easily be half a size or more.

So measure — or take your reading — at the end of the day, at normal room temperature, when hands are neither cold nor just exercised. That is the closest thing to an average, and it is the size a ring should be made to. A ring sized on a January morning will feel tight for most of the year.

Two things that change the answer

Band width. A wider band fits tighter than a narrow one in the same nominal size, because it covers more of the finger and has less room to flex over the knuckle. Anything above about 6mm typically needs a quarter to a half size up. Standard ring sizers are around 3mm, so a measurement taken on one under-reads a wide band.

Knuckles. If her knuckle is noticeably larger than the base of her finger, the ring has to be sized to clear the knuckle — and it will then be loose at the base and spin. This is common and entirely solvable: a jeweller can add sizing beads or a small internal bar to hold the ring in position without changing the size that passes over the knuckle. It is worth flagging at the design stage rather than discovering afterwards.

If you get it wrong

It is not a disaster, and it is worth saying plainly: nobody remembers the size the ring was on the day. Every Montare ring includes one free resizing within the first 60 days, and we support resizing beyond that for the life of the ring. A half-size off is a straightforward fix.

Two caveats to know in advance. Rings with stones set all the way around the band — full eternity styles — cannot easily be resized, because there is no plain section of shank to cut and rejoin, so those are worth getting right the first time. And it is generally easier to size a ring down than up, which is why guessing slightly large is the safer error. If in real doubt, we can build the ring and fit it properly afterwards.

The design and the diamond are the decisions that actually matter, and you can plan both in the ring builder or with a consultation. With the ring sorted, plan the moment itself with our guide to proposal ideas in Toronto, and see can you resize an engagement ring for the full detail.

Frequently asked questions

What is the average women's ring size?

Most women's ring sizes fall between US 5.5 and 7, with 6 to 6.5 the most common. If you have no measurement at all, 6.5 is a sensible default to size from.

How can I measure her ring size secretly?

Borrow a ring she already wears and measure its inside diameter, or wrap string around her finger while she sleeps and measure the length. Both avoid asking. A ring from her right hand usually runs about a half size larger than the left.

What if she is between sizes?

Choose the larger size — a slightly loose ring is more comfortable and easier to resize down than up.

Can a Montare ring be resized later?

Yes. Every ring includes a free resizing within 60 days, and we support resizing beyond that for the life of the ring. Full eternity bands are the exception, as stones running the whole way around leave no plain shank to work with.

What time of day should I measure a ring size?

The end of the day, at normal room temperature. Fingers are smallest when cold and first thing in the morning, and largest in heat, after exercise, after salty food and late in the day — a swing that can easily exceed half a size.

How do I convert millimetres to a ring size?

Inside diameter is the universal measure: 15.7mm is a US 5, 16.5mm is a US 6, and 17.3mm is a US 7. To get diameter from a circumference measurement, divide by 3.14. Half sizes are about 0.4mm of diameter apart.

Does band width change the ring size needed?

Yes. A wider band covers more of the finger and has less room to flex over the knuckle, so anything wider than about 6mm usually needs a quarter to half size up. Standard sizers are around 3mm and will under-read a wide band.

What if her knuckle is bigger than her finger?

The ring has to be sized to pass over the knuckle, which leaves it loose at the base. A jeweller can fit sizing beads or a small internal bar to stop it spinning without changing the size that clears the knuckle — best raised while the ring is being made.

Get it right. Order a free ring sizer, or design the ring in the ring builder.