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Ring Size Converter: US, UK, EU and Japanese Sizes

Updated By Tom Fairbairn

Type your size in one system and the converter finds the closest size in the others: US and Canada, UK and Australia, EU, Japan, and the inside diameter and circumference in millimetres. The table underneath shows every size from US 3 to US 14 in half steps, so you can also read it directly.

Convert your size

Ring sizes from US 3 to US 14
US / Canada UK / Australia EU (ISO) Japan Inside diameter (mm) Inside circumference (mm)
3 F 44 4 14.07 44.2
3½ G 45 5 14.47 45.5
4 H 47 7 14.88 46.8
4½ I 48 8 15.29 48.0
5 J½ 49 9 15.69 49.3
5½ K½ 51 10 16.10 50.6
6 L½ 52 12 16.51 51.9
6½ M½ 53 13 16.91 53.1
7 N½ 54 14 17.32 54.4
7½ O½ 56 15 17.73 55.7
8 P½ 57 16 18.13 57.0
8½ Q½ 58 18 18.54 58.2
9 R½ 60 19 18.95 59.5
9½ S½ 61 20 19.35 60.8
10 T½ 62 21 19.76 62.1
10½ U½ 63 22 20.16 63.3
11 V½ 65 24 20.57 64.6
11½ W½ 66 25 20.98 65.9
12 X½ 67 26 21.38 67.2
12½ Z 68 27 21.79 68.5
13 Z½ 70 29 22.20 69.7
13½ Z+1 71 30 22.60 71.0
14 Z+2 72 31 23.01 72.3

How the table is calculated

Every row starts from the US size. A US size 0 ring is 11.63 mm across the inside, and each whole size adds 0.8128 mm, so a US 7 is 17.32 mm across. The circumference is that diameter times pi.

  • EU sizes follow ISO 8653, which defines the size as the inside circumference in millimetres, rounded here to the nearest whole number.
  • UK letters come from the tables UK jewellers publish today, which start at A = 37.8 mm around. The old British standard that set the letters was withdrawn in 1993, so charts can disagree by half a letter, especially at the very small and very large ends.
  • Japanese sizes follow the common system in which size 1 is 13 mm across and each size adds a third of a millimetre. Some charts round differently from about size 18 up.

These are the published standards and the most common retail tables. They are not a guarantee of fit: a 7 mm wide band like the One Ring feels tighter than a thin band of the same size, and makers' own charts vary. When a retailer publishes its own conversion, use theirs.

Measuring your finger

The converter is only as good as the number you put in. The most reliable measurement comes from a jeweller's metal ring sizer, ideally one with a band about as wide as the ring you plan to buy. Measure at the end of the day, at room temperature, and if your knuckle is larger than the base of your finger, choose a size between the two.

Our One Ring size guide explains each step and lists the sizes each retailer actually offers. If you are choosing between metals, tungsten vs gold vs silver explains why a tungsten ring cannot be resized afterwards, and the wedding bands guide covers fit for a ring you will wear every day.

Frequently asked questions

Is a US size 7 the same everywhere?

Close, but not exactly. There is no single legal US standard, and retailers round differently, so two charts can disagree by a quarter or half size. Always check the retailer's own chart before ordering.

What is EU ring size?

The European size, defined in ISO 8653, is simply the inside circumference of the ring in millimetres. A size 54 ring measures about 54 mm around the inside.

Why do UK charts disagree?

The British standard that defined the letters was withdrawn in 1993, and retailers now use slightly different tables. The difference is usually half a letter.

Can I convert a Japanese size?

Yes. The common Japanese system starts at 13 mm inside diameter for size 1 and adds a third of a millimetre per size. Some charts round differently above size 18.