Ring sizes by country, and how to convert them
Ring sizes differ by country because each region uses its own scale. The US and Canada use numbers from 3 to 13, the UK and Australia use letters from A to Z, and most of Europe uses the inner circumference in millimeters under the ISO 8653 standard. Japan uses its own numbered scale. To convert, match the one number they all share: the inner circumference in millimeters.
You found the perfect ring on a UK site, and the size is a letter. Or a relative in Tokyo wants to send one, and the size is a number you do not recognize. Ring sizing is not standard across the world, so a US 7 is not a UK 7 or an EU 7. The good news: every system is really measuring the same circle, so you can always convert through millimeters.
Why are ring sizes different in each country?
Because the systems grew up separately, and each picked a different way to label the same circle. The US chose a numeric scale where each size step is a fixed jump in diameter. The UK chose letters of the alphabet. Europe took the simplest route and just used the inner circumference in millimeters as the size, so a size 54 ring measures 54 mm around the inside. None is more correct. They are different labels for the same physical ring.
What ring size system does each country use?
There are four main systems, and most countries use one of them:
- US and Canada: numbers from about 3 to 13, in half and quarter steps. Each step is a set change in diameter.
- UK, Ireland, and Australia: letters from A to Z, sometimes with a half size between letters.
- Europe (ISO 8653): the inner circumference in millimeters is the size. A size 54 ring is 54 mm around the inside.
- Japan (JIS): a numbered scale of its own, based on the inner diameter in millimeters.
The European system is set by ISO 8653, the international standard that defines a ring size as its inner circumference in millimeters. That is why an EU size looks like a plain measurement. Japan follows a similar idea under its JIS standard but lands on different numbers.
How do I convert ring sizes between countries?
Convert through the inner circumference in millimeters, the one value every system shares. Measure or look up the millimeters for your known size, then read across to the size you need. As rough anchors, a US 6 is about a UK L and an EU 51.5, a US 7 is about a UK N and an EU 54, and a US 8 is about a UK Q and an EU 57. For the exact row, use a chart rather than the eye.
- Find the inner circumference in millimeters for the size you already know.
- Look up that circumference on a conversion chart that lists US, UK, and EU side by side.
- Read across to the country you need. The millimeters are the anchor, so they always match.
- If you only have a ring, measure its inside diameter and convert that to circumference first.
The ring size chart lists every US size with its diameter and circumference in millimeters and the matching UK, EU, and Japan sizes, so you can convert in one place. To get your size from scratch, the printable ring sizer reads it directly, and how to measure ring size at home covers the string method if you have no printer.
Find your size in two minutes
Print a true-scale sizer with a built-in scale check, or convert a millimeter measurement on the page.