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Size chart

International ring size conversion

Enter a size in any system, or a millimetre measurement, and read the US, UK, EU, and Japan equivalents together. The math runs in your browser.

US / Canada
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UK / AU
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EU / ISO
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Japan
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Diameter
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Circumf.
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Convert through millimetres

Ring sizes don't convert cleanly between countries because every system was invented on its own terms, and only one of them, the European standard, is built from an actual measurement. The reliable way to convert is to go through millimetres: measure the ring's inner diameter or circumference, then map that single number onto each country's scale. The converter on the homepage does this in both directions; here is what the systems actually mean.

  • United States / Canada uses a numeric scale with half and quarter sizes (3, 3.5, 4…). Each full size is about 0.81 mm of inner diameter, or 2.55 mm of circumference, apart. The numbers are conventional; they don't equal any measurement directly.
  • UK / Ireland / Australia uses an alphabetical scale (A, B, C…, with half sizes). Each letter-step is about 1.25 mm of circumference. Because it's a different granularity than the US scale, US-to-UK conversions land on half-letters and vary by up to half a size between charts, so use the letter as a guide, not gospel.
  • Europe (ISO 8653) is the cleanest system: the size number is the inner circumference in millimetres. A size-54 ring measures 54 mm around the inside, per the ISO 8653 standard. Used across France, Germany, Italy, Spain, the Nordics, and most of Continental Europe. Note this is circumference, not the diameter you'd read off an existing ring.
  • Japan / China / India use numeric scales not linearly tied to diameter. In practice a Japanese size is roughly double the US size (US 7 ≈ JP 14, US 10 ≈ JP 20), but treat that as an approximation.
A few common conversions to anchor on: a US 6 ≈ UK L½ ≈ EU 52 ≈ JP 11–12; a US 7 ≈ UK N½ ≈ EU 54 ≈ JP 14; a US 10 ≈ UK T½ ≈ EU 62 ≈ JP 20. Because the systems round differently, nail the millimetre measurement first and let the converter handle the rest.

Full conversion table

US / CA UK / AU EU / ISO Japan Diameter (mm) Circumf. (mm)
3 F 44 4 14.1 44.2
3.5 G 45 5 14.5 45.4
4 H 47 7 14.9 46.7
4.5 I 48 8 15.3 48.0
5 J½ 49 9 15.7 49.3
5.5 K½ 51 10 16.1 50.5
6 L½ 52 12 16.5 51.8
6.5 M½ 53 13 16.9 53.1
7 N½ 54 14 17.3 54.4
7.5 O½ 56 15 17.7 55.6
8 P½ 57 16 18.1 56.9
8.5 Q¼ 58 18 18.5 58.2
9 R½ 59 19 18.9 59.5
9.5 S½ 61 20 19.4 60.7
10 T½ 62 21 19.8 62.0
10.5 U½ 63 22 20.2 63.3
11 V½ 65 24 20.6 64.6
11.5 W½ 66 25 21.0 65.8
12 X½ 67 26 21.4 67.1
12.5 Y½ 68 27 21.8 68.4
13 Z½ 70 29 22.2 69.7
13.5 Z1½ 71 30 22.6 70.9

UK letters and Japan sizes are approximate; see the full chart and the methodology for sourcing.

Common questions

Why are ring sizes different in each country?

Each system was built independently. The US uses a numeric scale with half and quarter sizes; the UK, Ireland, and Australia use an alphabetical scale (A, B, C…); most of Continental Europe uses the ISO 8653 system, where the size number is literally the inner circumference in millimeters; and Japan, China, and India use their own numeric scales. Because millimeters are the one thing every ring physically has, converting through the millimeter measurement is the reliable way across systems.

How do I convert a US ring size to UK?

UK uses letters, so a US 6 is roughly a UK L½, a US 7 a UK N½, and a US 10 a UK T½, because each full US size is about two UK letter-steps. UK letter charts vary by up to half a size between sources, so for an important purchase, confirm the millimeter measurement rather than relying on the letter alone.

What is a US 7 in European ring size?

About a European (ISO) size 54. Under ISO 8653 the size equals the inner circumference in millimeters, and a US 7 has an inner circumference of roughly 54.4 mm, so it rounds to EU 54. A US 6 is about EU 52 and a US 10 about EU 62.

How does Japanese ring sizing work?

Japan uses a numeric scale that isn't linearly tied to diameter, but in practice a Japanese size is roughly double the US size: US 5 is about JP 9, US 7 about JP 14, and US 10 about JP 20. Treat these as close approximations and confirm with a millimeter measurement when precision matters.

What is the most reliable way to convert between ring size systems?

Convert through millimeters. Every ring has a fixed inner diameter and circumference in millimeters, so measuring that and mapping it to each country's scale avoids the rounding disagreements between letter-and-number charts. Enter your millimeter measurement into a converter to get every system at once.

Do European ring sizes use diameter or circumference?

Circumference. The European ISO 8653 standard defines the ring size as the inner circumference in millimeters, so a size 54 ring measures 54 mm around the inside. That's different from measuring an existing ring by its diameter (across the middle), so don't confuse the two: a 54 mm circumference is only about a 17.2 mm diameter.