International ring size conversion chart, every system compared
Every ring sizing system in the world is describing the same physical thing — the inside circumference of the ring — just labeled on a different scale. This ring size conversion chart cross-references the major systems against that single shared measurement, so you can look up a size in one country and find its match anywhere else. For a deeper look at any single system, see our full US, UK, or Japan ring size charts.
Quick reference: US 7 = UK N = Japan 14 = 54.4mm · US 6 = UK L = Japan 12 = 51.9mm · US 9 = UK R = Japan 19 = 59.5mm · US size 13 = UK Z = Japan 29 = 69.7mm — search the full table below for any other size.
| US / Canada | UK / AU / NZ | Japan / China | EU / ISO (mm) | Diameter (mm) |
|---|---|---|---|---|
| US 3 | UK F | 4 | 44.2 mm | 14.1 mm |
| US 3.5 | UK G | 5 | 45.5 mm | 14.5 mm |
| US 4 | UK H | 7 | 46.8 mm | 14.9 mm |
| US 4.5 | UK I | 8 | 48.0 mm | 15.3 mm |
| US 5 | UK J | 9 | 49.3 mm | 15.7 mm |
| US 5.5 | UK K | 10 | 50.6 mm | 16.1 mm |
| US 6 | UK L | 12 | 51.9 mm | 16.5 mm |
| US 6.5 | UK M | 13 | 53.1 mm | 16.9 mm |
| US 7 | UK N | 14 | 54.4 mm | 17.3 mm |
| US 7.5 | UK O | 15 | 55.7 mm | 17.7 mm |
| US 8 | UK P | 17 | 57.0 mm | 18.1 mm |
| US 8.5 | UK Q | 18 | 58.3 mm | 18.5 mm |
| US 9 | UK R | 19 | 59.5 mm | 18.9 mm |
| US 9.5 | UK S | 20 | 60.8 mm | 19.3 mm |
| US 10 | UK T | 22 | 62.1 mm | 19.7 mm |
| US 10.5 | UK U | 23 | 63.4 mm | 20.1 mm |
| US 11 | UK V | 24 | 64.6 mm | 20.5 mm |
| US 11.5 | UK W | 26 | 65.9 mm | 20.9 mm |
| US 12 | UK X | 27 | 67.2 mm | 21.3 mm |
| US 12.5 | UK Y | 28 | 68.5 mm | 21.7 mm |
| US 13 | UK Z | 29 | 69.7 mm | 22.1 mm |
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Open the converterIndia commonly follows the same letter-based scale as the UK, though some jewelers there also use the US numeric scale — it's worth confirming which one a specific retailer means. China and much of the rest of Asia generally align closely with Japan's numeric scale, but not always exactly, so local confirmation matters for anything you can't easily resize. Switzerland and other parts of continental Europe sometimes use sizing conventions distinct from the standard EU/ISO circumference figure shown here — when in doubt, ask the jeweler which specific scale their listed number refers to.
There's no single global governing body that unifies ring sizing the way there is for, say, shoe sizing under ISO standards worldwide. Instead, each region standardized its own scale independently, and ISO 8653:2016 exists as a reference point that most — but not all — national systems can be cross-checked against. That's the gap this chart is built to close.
The chart above is only as good as the measurement you start with. Our complete measuring guide covers the string, paper, and existing-ring methods in detail, and our existing-ring tool converts a diameter instantly if you already own a ring that fits. Worth knowing before you measure: temperature and time of day genuinely affect the reading, and wide bands typically need sizing up compared to a thin band at the same labeled size.
If it's difficult or impossible to resize the ring you're buying, check what can and can't be resized before you order across borders. Sizing something as a surprise? Our engagement ring sizing guide covers how to get a reliable estimate discreetly.
Find your size in any one column — US, UK, Japan, or EU/ISO millimeters — and read across the same row for its equivalent in every other system. Use the search box above to jump straight to a specific size, or use our converter if you'd rather enter a measurement directly.
Your ring size in millimeters is its inside diameter or inside circumference — the two right-hand columns in the chart above. A US size 7, for example, has an inside diameter of about 17.3mm and an inside circumference of about 54.4mm.
EU and ISO sizes are typically given as the inside circumference in millimeters directly, while US sizes use a separate numeric scale — so a US 7 corresponds to roughly 54mm, and a US 9 to roughly 59.5mm. See the EU/ISO column above for the exact match to any US size.
No — there's no single global governing body the way there is for shoe sizing. ISO 8653:2016 exists as a reference point that most national systems can be cross-checked against, which is what this chart is built around, but each country's own labeling scale (US, UK, Japan) remains distinct.
The UK's letter scale is also used in Ireland and Australia, and commonly in India as well. Japan's numeric scale is widely used as a practical reference across China and other parts of Asia, though not always identically. The US and Canada share the identical numeric scale with no conversion needed.
Free ring size conversion and measurement tools for US, UK, Japan, and international sizing systems.
© Rings Sizer. Sizes are estimates — confirm in person for a permanent purchase.