Ring Size Conversion: US, UK, EU, Japan

Ring sizing is the single most common cause of returns in online jewellery sales, and almost all of it comes down to two problems: buyers measure at the wrong moment, and sellers publish conversion tables that do not agree with each other.

The table below uses the ISO 8653 definition, where the European size is simply the inner circumference in millimetres. That makes it the most reliable anchor point, because every other system can be derived from it. Diameters are rounded to one decimal place.

Ring size conversion table

US / Canada	UK / Australia	EU (ISO 8653)	Japan	Inner diameter	Inner circumference
4	H	46.8	7	14.9 mm	46.8 mm
4.5	I	48.0	8	15.3 mm	48.0 mm
5	J	49.3	9	15.7 mm	49.3 mm
5.5	K	50.6	10	16.1 mm	50.6 mm
6	L	51.9	11	16.5 mm	51.9 mm
6.5	M	53.1	12	16.9 mm	53.1 mm
7	N	54.4	13	17.3 mm	54.4 mm
7.5	O	55.7	14	17.7 mm	55.7 mm
8	P	57.0	15	18.2 mm	57.0 mm
8.5	Q	58.3	16	18.6 mm	58.3 mm
9	R	59.5	17	19.0 mm	59.5 mm
9.5	S	60.8	18	19.4 mm	60.8 mm
10	T	62.1	19	19.8 mm	62.1 mm
10.5	U	63.4	20	20.2 mm	63.4 mm
11	V	64.6	21	20.6 mm	64.6 mm
11.5	W	65.9	22	21.0 mm	65.9 mm
12	X	67.2	23	21.4 mm	67.2 mm
12.5	Y	68.5	24	21.8 mm	68.5 mm
13	Z	69.7	25	22.2 mm	69.7 mm

A quick sanity check: the European number equals the circumference, and the circumference equals the diameter multiplied by pi. If a table you find online does not satisfy that, it is unreliable.

Size converter

Enter an inner diameter or an inner circumference and the other systems are calculated from it.

For a one-step conversion from a single millimetre measurement, the ring size calculator turns it into US, UK, EU and JP sizes.

Inner diameter (mm)

Inner circumference (mm)

US / Canada: —

UK / Australia: —

EU (ISO 8653): —

Japan: —

Printable ring sizer

Print this at 100% scale with page scaling turned off, then place a ring you already own over the circles and match the inner edge. Check the scale afterwards by measuring the printed scale bar with a ruler — if the bar is not exactly 50 mm, your printer is scaling the page and every measurement will be wrong.

How to measure a finger correctly

The string method, done properly

Wrap a strip of paper or non-stretch string around the base of the finger, mark where it overlaps, then measure the length. That is the circumference. Do not pull it tight — it needs to pass over the knuckle.

Measuring an existing ring

Measure the inner diameter across the widest point, not the outer. Callipers are ideal; a ruler works if you measure carefully. If the ring is a wide band, read the next section before you convert.

Use a ring mandrel if you have one

A metal or plastic mandrel is the standard tool in a workshop and the most consistent method. Push the ring on and read the size where it stops, applying light pressure only.

Why measurements go wrong

• Time of day. Fingers swell in the afternoon and in warm weather. Measuring in the morning gives a smaller reading than measuring at night, by as much as half a size.
• The knuckle. The ring has to pass the knuckle, so if the knuckle is much larger than the base, size for the knuckle rather than the base.
• Wide bands. A band wider than about 6 mm needs roughly half a size larger than a narrow band on the same finger, because more of the finger is in contact with metal and there is less give.
• Stacking. If the ring will be worn stacked next to others, the knuckle becomes the limiting factor again.
• Units. Confirm whether a supplier quote is a diameter or a circumference. This single ambiguity causes more sizing errors than any other factor.

What this means if you are buying wholesale

If you are stocking a range rather than making to order, the distribution matters more than any single size. The pattern most sellers see:

• Women's ranges concentrate heavily in the middle of the table. US 6 and 7 together typically account for the largest share of any women's assortment.
• Men's ranges centre around US 9 to 10, with a wider spread at the top end.
• US 5 and US 11 and above sell slowly but are the sizes customers remember finding, so carrying a small quantity pays off in goodwill.

Open-ended and adjustable designs sidestep the problem entirely, which is why they are common in entry-level stainless steel ranges. If you are planning a first order, ask your supplier which sizes they hold in stock, because a minimum order quantity that looked reasonable across a full size run can look very different when it is split across nine sizes.

What ring size is 17.3 mm?

An inner diameter of 17.3 mm is US 7, UK N, EU 54.4 and Japan 13. The circumference is 54.4 mm.

What ring size is 54 mm?

A circumference of 54 mm is EU 54, which sits between US 6.5 (53.1 mm) and US 7 (54.4 mm). Most people would take US 7, since sizing up slightly is more comfortable than sizing down.

Are EU ring sizes the same as millimetres?

Yes, under ISO 8653 the European size is the inner circumference in millimetres. This is why the EU column in the table above matches the circumference column exactly.

What sizing system does China use?

Mainland China commonly sizes rings by inner circumference in millimetres, which is the same basis as the ISO and European system. Hong Kong uses a separate numbered scale that runs close to the Japanese one, so if a supplier quotes a Hong Kong size, confirm the basis before converting.

Should I size up for a wide band?

Yes. For a band wider than roughly 6 mm, go up about half a size from your usual measurement. The extra contact area makes a snug fit uncomfortable and harder to remove.

Why do two conversion charts disagree?

Usually because one is quoting diameter and the other circumference, or because a chart has been rounded repeatedly as it was copied between sources. Check whether the circumference equals the diameter multiplied by pi. If it does not, the chart is wrong.

Can stainless steel rings be resized?

Not in the way gold or silver can. Stainless steel is hard and work-hardens, so cutting and re-joining a band is impractical for most workshops. Getting the size right the first time matters more with steel than with softer metals. For more on the material, see our comparison of 316L and 304 stainless steel in jewellery.

A note on packaging

Ring boxes are sized around a standard slot width rather than around the ring itself, so a conversion chart will not tell you which insert you need. If you are matching rings to packaging, the slot width and the insert material matter more than the ring size — covered in our guide to choosing a jewellery box for rings.

Download or share this chart

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Multi-region ring size chart (US, UK, EU, Japan)

A printable chart covering the US, UK, EU (ISO 8653) and Japan systems, with a per-market note on reading each scale. Use it alongside the converter above.

Download the multi-region ring size PDF

The embeddable chart (ring-size-multiregion-embed.html) can be hosted on your own site or iframed, and links back to this guide — a simple way to offer a size tool to your visitors.

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Frequently Asked Questions

Why do ring conversions confuse online buyers?

Because the charts measure three different things. Some convert circumference, some convert diameter, and the figures are close but not identical. A buyer comparing two charts gets two sizes and picks badly.

Which measurement should a listing publish?

The inside diameter in millimetres alongside the size in the market you sell in. Diameter is the figure that stays comparable between suppliers, and it is the one a buyer can check with a caliper.

What should go in the box to reduce returns?

The size printed on the insert card, plus a sizing ring. Sizing returns almost all come from a buyer guessing, and a printed size removes the guess before the order is even placed.

What this means for your order

If you are still deciding, one thing decides this for you: which region your customer is sizing for; a single chart is the reason returns happen, because a US and a Japanese ring size are not the same measurement wide. Everything else on a quote page is presentation.

Where this falls short no value if the shop sells in one region only and already prints the right chart.

What to send us Tell us your sales regions and we will tell you which columns the chart needs to cover.