How to Find Your Ring Size

By Dmitry Strugovshchikov, founder of STRUGA

Your ring size is the inner diameter of the ring in millimetres. If a ring sits comfortably on the finger and measures 18 mm across the inside, that is your size — 18 mm. Countries put different labels on top of this number (US numbers, UK letters, EU circumference), but the diameter in millimetres is the same everywhere. It is the one figure you can read at home with a ruler and a strip of paper in two minutes.

This guide is the full breakdown: how ring sizing works across countries, how to measure your finger accurately in four ways, how to convert between US, UK and EU systems, which mistakes spoil a measurement, and how STRUGA fits the size when casting. At the end — a conversion table and answers to common questions.

- A ring size is the inner diameter of the band in millimetres; US numbers, UK letters and EU circumference are only labels on that same figure.

- Without a ring, wrap the finger with thread or a paper strip, measure the circumference and divide by 3.14 to get the diameter.

- Most adults fall between roughly 15.5 and 22 mm in diameter; a 56.5 mm circumference equals an 18 mm size (about US 7.5).

- Measure in the evening when hands are warm, and for a wide ring (6 mm and up) go half a size larger.

- STRUGA rings are made by hand in 925 silver — wax model, silicone mould, 925 silver, hand finishing — and the exact size is confirmed at order.

- A non-standard size, wide brutal models such as BRUTALISM V.1 or THORN, and paired DARK UNION rings are cast to size through Custom Order.

How ring sizing works — and why millimetres are the anchor

Underneath every system, a ring size is one physical thing: the inner diameter of the band. A size that measures 17 mm across the inside is 17 mm wide, full stop. The systems differ only in how they label that diameter.

In the US (and Canada) sizes are numbers — 5, 6, 7, with halves — not tied directly to millimetres. In the UK and Australia they are letters — J, K, L. In Europe the size is the inner circumference in millimetres (diameter × 3.14), so EU 57 means a 57 mm circumference. Because the labels do not line up perfectly, the safe move when ordering abroad is to work from the diameter in millimetres — the figure that is identical everywhere.

Most adults fall between roughly 15.5 and 22 mm in diameter. Women's sizes cluster lower, men's higher — but that is only a starting point. Fingers differ, and the only reliable answer is to measure.

How to measure your ring size at home — four ways

1. From a ring that fits (most accurate)

If you have a ring that wears comfortably on the right finger:

• Lay it on a ruler and measure the inner diameter — the distance between the inside walls at the widest point.
• That number in millimetres is your size. An inner diameter of 17.5 mm means a 17.5 mm size (about US 7).
• Measure the inner edge, not the outer — the thickness of the walls does not count.

This is the most honest method: the ring has already taken the shape of your finger and knuckle into account.

2. With thread or a paper strip

If you have no ring, measure the finger itself:

• Take a thread or a paper strip 3–5 mm wide. Wrap it around the base of the finger — where the ring will sit.
• Mark where the end overlaps the start. Unroll it and measure the length to the mark — that is the circumference of the finger.
• Divide the circumference by 3.14 (pi). The result is the inner diameter — your size.

Example: a circumference of 56.5 mm ÷ 3.14 = 18 mm, a size of 18 (about US 7.5).

3. A printable ring sizer

Jewelry sites offer printable sizers: a sheet with rings of different diameters printed on it (to check against your own ring), or a paper strip to wrap the finger. Print strictly at 100% scale, without "fit to page" — otherwise the diameters distort. After printing, hold a ruler against the control line on the sheet and confirm the scale is exact.

4. At a jeweller

The most precise measurement is a jeweller's ring gauge — a set of reference rings or a marked tapered mandrel. If a ring is expensive or made to order, it is worth one visit to learn your size exactly. After that, the number is yours for good.

Ring size conversion: US, UK, EU and millimetres

The inner diameter in millimetres converts to the other systems like this:

Diameter (Ø mm)	Circumference (mm)	US	UK	EU
15.5	48.7	5	J	48–49
16.0	50.3	5.5	K	50
16.5	51.8	6	L	52
17.0	53.4	6.5	M	53
17.5	55.0	7	N	55
18.0	56.5	7.5	O	56–57
18.5	58.1	8.5	P	58
19.0	59.7	9	Q	59–60
19.5	61.3	9.5	R	61
20.0	62.8	10	S	62–63
20.5	64.4	10.5	T	64
21.0	66.0	11.5	U	66
22.0	69.1	12.5	W	69

Conversions between countries are rounded — the systems do not step in perfect lock. When ordering from abroad, always go by the diameter in millimetres: it is the one value that is the same everywhere.

Common measuring mistakes

Measuring in the morning or in the cold. Fingers narrow in the cold and toward the morning, and widen in warmth and toward the evening — the difference can reach half a size. Measure in the evening, at room temperature, when your hands are warm. Then the ring will not slip on an ordinary day.

Ignoring the knuckle. The joint is often wider than the base of the finger. The ring has to pass over the knuckle but not spin at the base. If the difference is large, aim for the size at which the ring comes off with light resistance.

Not accounting for the width of the ring. A narrow band (2–3 mm) and a wide one (6–10 mm) of the same size sit differently: the wide one is tighter. For a massive ring, go half a size larger. This matters most for the brutal models — for example Brutalism V.1 or Thorn.

Measuring with a thin thread pulled tight. A thread that is too thin cuts in and stretches, giving a low reading. Use a paper strip as wide as the future ring, and do not pull it tight.

Which finger, which hand

The same finger on the right and left hand can differ by half a size — the working hand is usually a touch larger. Measure the exact finger and hand you will wear the ring on. Which hand a wedding or engagement ring goes on differs by country and tradition, so size for the hand you actually intend to use.

Ring sizes at STRUGA — how we work

STRUGA rings are made by hand in oxidised 925 silver: a wax model, a silicone mould, 925 silver, and hand finishing. Catalogue models come in a standard size range, and we confirm the exact size when the order is placed, so the ring sits the way it should.

If your size is not in stock, or you need a non-standard fit, we cast the ring to your size through Custom Order. The same goes for the wide, brutal models, where fit matters most. Paired rings for engagement and marriage, each made to its own size, sit in the Dark Union line.

See the current models in the rings collection: from the minimal Signature Links to the Heart Lock. If you are unsure of your size, write to us before ordering — we will help you work it out.

Frequently asked questions

Is a ring size the same as a country size like US or EU?

No. A ring size is one physical thing — the inner diameter of the band in millimetres. US numbers, UK letters and EU circumference are different labels placed on that same diameter, which is why they do not line up perfectly. When ordering abroad, work from the diameter in millimetres: it is the one figure that is identical everywhere.

Is the EU size the same as the diameter in millimetres?

No. The EU size is the inner circumference, not the diameter — EU 57 means a 57 mm circumference, which is a 57 ÷ 3.14 ≈ 18 mm diameter. The diameter is the anchor; the EU number is the circumference label on it.

Is finger circumference the same as ring size?

Not directly. The circumference is what you measure by wrapping the finger; the ring size is the diameter you get after dividing that circumference by 3.14. A 56.5 mm circumference is an 18 mm size, not size 56.

Is a printable ring sizer reliable?

Only if printed at exactly 100% scale. Printed with "fit to page", the diameters distort and the reading is wrong. After printing, hold a ruler against the control line on the sheet and confirm the scale before trusting it.

Can you find your ring size by eye, without measuring?

Not reliably. A visual guess is off by one or two sizes, and that is the difference between "fits" and "slips off." The minimum honest method is to wrap the finger with thread and divide the circumference by 3.14. It takes two minutes and needs nothing but a ruler.

What if your size falls between two values?

Round up, especially for a wide ring. A ring that is a little loose can be worn; one that is too tight will not go on and will press the finger. Between 18 and 18.5 mm, when in doubt, take 18.5.

Is the size the same on the right and left hand?

Often not. The working hand (the right, for right-handed people) is usually half a size larger. Measure the hand and finger you will actually wear the ring on.

How do I convert a millimetre diameter to a US size?

By the table above: the diameter in mm is the anchor, the US size is a label on it. For example, 17.5 mm ≈ US 7, and 19.5 mm ≈ US 9.5. When ordering, go by the diameter in millimetres — it does not depend on the country.

Can the size of a ring already bought be changed?

A plain, smooth ring can usually be sized up or down by one or two sizes by a jeweller. Rings with complex texture, settings or a solid cast form are harder to alter — sometimes it is simpler to recast. So an exact measurement before ordering saves time and money.

What ring size is considered average?

For women it is most often around 16.5–18 mm, for men around 19.5–21 mm. But "average" is no reason to guess: the spread within those ranges is wide, and the only exact answer comes from measuring your finger.

In short

A ring size is the inner diameter of the band in millimetres, and that is where the simplicity lies. Measure a ring you already have with a ruler, or wrap the finger with thread and divide the circumference by 3.14. Measure in the evening, account for the width of the ring and the knuckle — and the size will be exact. And if your size is not in stock, we will cast the ring to fit you.