Ring Sizes Around the World

What a ring size measures

Every ring size comes from one of two lengths: the inner circumference, the distance around the inside of the band, or the inner diameter, the distance straight across. The two are tied by pi, so a circumference of 54.4 mm is a diameter of 17.3 mm, but a system that counts one gives a different number from a system that counts the other. Europe counts the circumference. Japan, Korea and the post-Soviet states count the diameter. The United States uses a numbered scale and Britain a run of letters, both derived from the same physical ring. Knowing which length a number stands for is most of the work of converting it.

Europe: one circumference, several labels

ISO 8653 sets the ring size as the inner circumference in whole millimetres, and holds each size to a diameter within a hundredth of a millimetre. France and Germany use that same number, so a ring is a 54 across Continental Europe and needs no conversion between those countries. Two traps hide in the detail. France once labelled rings as the circumference minus forty, a pre-metric form that still appears on vintage pieces, so an old French 14 is a modern 54. Germany sometimes prints the diameter beside the circumference, as 54 over 17.3, and a buyer who reads the smaller number as the size orders a ring far too small.

Japan and Korea: the gou scale runs on diameter

Japan sizes rings on the 号, read gou, and Korea on the 호, read ho, and the two are one scale with no offset. It is built on the inner diameter, not the circumference. Size 1 is a 13.0 mm bore, and every step up adds a third of a millimetre of diameter, so the diameter of size n is 13.0 plus (n minus 1) divided by three. A US 7, at 17.3 mm across, works out to a Japanese 14, and a US 6 to a 12. This is why an English chart that calls the Japanese size a circumference gets it wrong by dozens of numbers: a 14 is a diameter reading, and the 54 beside it is the European circumference of the same ring. Japan also keeps a metric scale, JIS S 4700, that numbers rings by whole millimetres of circumference like ISO, where the number is the gou plus forty. Japanese consumer charts often take a shortcut, reading the number as the circumference in millimetres less about 39, which runs roughly one size high against the exact diameter, so a ring a jeweller measures as a 12 by diameter can be quoted as a 13 on a shop chart. The diameter is the definition and the shortcut is the approximation. Modern Korean shops sometimes quote the millimetre circumference too, so a Korean size can be either the ho number or the millimetre figure, worth checking before you order.

Russia and the CIS size by diameter

Russia, Ukraine and the wider CIS label a ring by its inner diameter in millimetres, rounded to the nearest half. A US 7 is a 17.5 there, the same 17.3 mm bore read to the nearest half millimetre, and the same ring Europe calls a 54. Because the post-Soviet number is a diameter and the European one a circumference, the two look nothing alike for one physical ring, which is the usual cause of a diaspora buyer ordering a size out.

Hong Kong and mainland China differ by about one

Hong Kong and mainland China both use small integer scales close to the circumference in millimetres with a constant taken off, near 39 for Hong Kong and 40 for the mainland, so a mainland number tends to sit one below its Hong Kong twin. Neither is standardised, and shops vary, so a cross-border chart can be off by a size or two. Many mainland sellers sidestep it by quoting the circumference in millimetres outright, which converts to Europe without any arithmetic.

The United States and Britain

The United States runs a numbered scale in half steps, where each full size adds about 2.55 mm of circumference, so US 6, 6.5 and 7 climb in even jumps. Britain uses a single alphabetical run, A through Z, then Z1 and Z2 for the largest, one letter to a half US size. Both are read off the same band as every other system, which is why the millimetre columns are the reliable bridge between them.

The international ring size table

Every column below comes from one 54.4 mm to 44 mm range of real rings. US, UK, ISO, diameter and Japanese numbers are from the catalog; Russia is the diameter to the nearest half; Hong Kong and mainland China are the circumference less 39 and 40, and are approximate.

Japanese and Korean numbers above 28, and all Hong Kong and mainland values, are approximate. Convert a specific size on the US to ISO (mm) or US to UK chart, or see all ring size charts.

What jewellers say the charts leave out

A conversion number is a starting point, and the trade adds the corrections a chart cannot. Jewellers size up about half a size for a band wider than 6 mm, and a quarter to a half more from 8 mm up, because a broad band sits flat against the finger and grips where a thin one slides. They measure warm and late in the day, since a finger can swell close to a full size between a cold morning and a hot afternoon. For a surprise, the standard move is to borrow a ring the person already wears and measure its inner diameter, rather than guess the finger. Jewellers who ship abroad give the same warning: for Hong Kong, mainland and old French numbers, size to the millimetre and confirm the measurement, because the country label alone can be a size or two out.

Converting a ring size without a mistake

Measure the band you have, or the finger, in millimetres, and treat that millimetre figure as the anchor. To reach a national size, read the number that country builds from that measurement rather than converting number to number across systems. In the catalog a 17.3 mm bore is a US 7, a UK N, an ISO 54 and a Japanese 14, and a 16.5 mm bore is a US 6, a UK L and an ISO 52. When a measurement lands between two sizes, the wider band takes the larger. For the measurement itself and the corrections, see the ring measuring guide.

Frequently asked questions

What is a Japanese ring size?

The Japanese 号 (gou) is the inner diameter, not the circumference. Size 1 is a 13.0 mm bore and each step adds a third of a millimetre, so a US 7 is a Japanese 14. Korea's 호 (ho) is the same scale.

Is EU ring size 52 a Korean 52?

No. EU 52 is a 52 mm circumference, which is a US 6 and a Japanese or Korean 12, not a 52. Korea and Japan number by diameter, so their figure is small.

What is EU ring size 52 in US?

A US 6. The European 52 is the inner circumference in millimetres, and the catalog maps that ring to a US 6, a UK L and a 16.5 mm bore.

Why do international ring charts disagree?

Because some number the circumference and some the diameter, and Hong Kong, mainland and old French scales take a constant off that are not standardised. The millimetre measurement is the value that never changes.

How do I size for a wide band?

Add about half a size for a band over 6 mm, and a quarter to a half more from 8 mm up, since a broad band grips more of the finger than a thin one.