Convert ring sizes across Japan, the US, the EU and the UK, or enter a measured inner circumference or diameter.
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Ring Size Table
Convert ring sizes across Japan, the US, the EU and the UK, or enter a measured inner circumference or diameter.
Data last maintained
About the ring size table
Measuring inner circumference and diameter
Two measurements describe a ring. Inner circumference is the length around the inside, easiest to get by wrapping a paper strip around the finger, marking where it overlaps and measuring the strip flat. Inner diameter is the distance straight across the inside of a ring you already own, best read with a caliper. The two are linked by circumference equals diameter multiplied by pi, so either one is enough to find a size.
How each sizing system is defined
ISO 8653 defines ring size as the inner circumference in millimetres, and the European number is exactly that value. JIS S 4700 in Japan follows the same definition. US and Canadian sizes advance in steps of about 2.55 mm of circumference per whole size, with half sizes in between. UK and Australian sizes use letters, one letter division being 1.25 mm of circumference. The Japanese 号 scale advances by one third of a millimetre of inner diameter per size.
Why the Japanese scale is a convention, not a standard
JIS S 4700 designates ring sizes only by inner circumference in millimetres, in the range 41 to 76, and never mentions the 号 scale. The 号 numbering used in shops across Japan and Taiwan is therefore a trade convention. Published tables from independent sources agree closely on its values, which is why it can be listed here, but it carries no standards body behind it. Where a jeweller works to a slightly different table, treat the millimetre columns as the reliable reference.
FAQ
Common questions and answers about this topic.
How do I measure my ring size at home?
Wrap a strip of paper around the base of the finger, mark the overlap, lay the strip flat and measure to the mark in millimetres. That figure is the inner circumference, which you can enter directly. If you already own a ring that fits, measure straight across its inside instead and enter that as the inner diameter.
What is US size 7 in Japanese and Taiwanese sizing?
US 7 corresponds to an inner circumference of about 54.5 mm, which is Japan and Taiwan size 14 and EU 54 or 55. Pick the row in the table to see every system at once; the equivalent for any other size is one selection away rather than something to memorise.
Should I measure the inner diameter or the inner circumference?
Measure whichever is easier for what you have. A paper strip around the finger gives the circumference; a caliper across an existing ring gives the diameter. They describe the same ring and are linked by circumference equals diameter multiplied by pi, so this tool accepts either. Circumference is usually more accurate for a bare finger because it follows the actual shape.
Why does the EU size look like the millimetre measurement?
Because it is. ISO 8653 defines ring size as the inner circumference expressed in millimetres, so a ring measuring 54 mm around the inside is EU size 54. Japan's JIS S 4700 uses the same definition. Systems that use their own numbering, such as the US and UK scales, have to be mapped back onto that millimetre value, which is why they rarely land on round numbers.
My measurement falls between two sizes. Which one should I take?
The tool shows the closest row and says the value sits between sizes. Which way to round is a judgement call rather than a calculation, so it is left to you. A ring has to pass the knuckle, and a wide band fits tighter than a thin one, so rounding up is the more common choice. Measuring again at a different time of day is worth doing before deciding.
What does this table cover, and what is out of scope?
It covers inner circumference and diameter in millimetres alongside the Japan and Taiwan, US and Canada, EU and UK and Australia systems, over the range the table lists. It does not carry brand-specific sizing, does not recommend or link to any seller, and does not account for band width, ring style or how a stone sits. Where a jeweller uses a slightly different chart, treat the millimetre columns as the reference.
Data Sources
This tool's data is compiled from the authoritative sources below.
- ISO 8653 - Jewellery: ring-sizes, definition, measurement and designation(opens in a new tab)
- JIS S 4700 ジュエリー用指輪のサイズ (full text)(opens in a new tab)
- Ring size - conversion relations between sizing systems(opens in a new tab)
Data last maintained