There is no single global ring sizing standard. The US uses numbers, the UK uses letters, Europe and most luxury brands use circumference in millimeters, India uses a separate numbered scale, and Japan uses yet another set of numbers. Shopping internationally, receiving a ring as a gift from abroad, or buying from a brand that lists only one system means you need to convert.
This is the master guide to ring size conversion. It covers all major systems with a combined chart, explains why each country developed its own scale, and shows you the fastest way to convert any size into the system you need.
International Ring Size Conversion Chart
| Inner diameter (mm) | US size | UK size | EU size | India size | Japan size |
|---|---|---|---|---|---|
| 14.9 | 4 | H | 46.8 | 8 | 7 |
| 15.3 | 4.5 | I½ | 48 | 9 | 8 |
| 15.7 | 5 | J½ | 49.3 | 10 | 9 |
| 16.1 | 5.5 | K½ | 50.6 | 11 | 11 |
| 16.5 | 6 | L½ | 51.9 | 12 | 12 |
| 16.9 | 6.5 | M½ | 53.1 | 13 | 13 |
| 17.3 | 7 | N½ | 54.4 | 14 | 14 |
| 17.7 | 7.5 | O½ | 55.7 | 15 | 15 |
| 18.2 | 8 | P½ | 57.2 | 16 | 16 |
| 18.6 | 8.5 | Q½ | 58.5 | 17 | 18 |
| 19.0 | 9 | R½ | 59.7 | 18 | 20 |
| 19.8 | 10 | T½ | 62.2 | 20 | 22 |
| 20.6 | 11 | V½ | 64.8 | 22 | 24 |
| 21.4 | 12 | X½ | 67.2 | 24 | 27 |
Why Ring Sizes Differ Between Countries
Each sizing system developed independently before international standardization was practical. The US adopted a numerical scale in the 1800s through jeweler trade guilds. The UK developed its alphabetical system separately, and European jewelers standardized around circumference measurement which is now the ISO standard for professional jewelers.
Japan and India developed their own scales separately based on local trade practices. None of these systems has been globally standardized yet, which is why conversion charts are still necessary. For a deeper look at this history, see our guide on why ring sizes differ between countries.
The Fastest Way to Convert Any Ring Size
The most reliable approach is to always work through the inner diameter in mm. That number is in every chart, understood by every jeweler, and does not depend on which country's convention is being used. Once you know your diameter in mm, you can enter any country's chart at the mm column and read across.
If you only have a size number or letter and need to convert, use the chart above to find your diameter first. That gives you a reliable anchor point. Then share the mm measurement with any jeweler, regardless of which system they use.
Converting Specific Systems
For US to UK specifically, see our detailed US to UK ring size conversion guide. For US to EU, see US to EU conversion. For EU to UK, see EU to UK conversion. For US to India, see US to India ring size conversion. For Cartier and European luxury brand sizing specifically, see our Cartier ring size guide. For Japanese sizing, see the Japan ring size guide. For Australian sizing, see the Australian ring size chart.
What to Do If a Conversion Does Not Come Out Exact
Ring size conversions do not always land on a clean number in the target system. When they fall between two sizes, the practical rule is to size up for wide bands or everyday rings, and size down only for narrow decorative bands where a tighter fit is acceptable.
For the most accurate starting point, measure your finger directly rather than converting a size you were told. Use our ring size calculator to get your measurement in all systems at once. For the full home measurement process, see how to measure ring size at home.
FAQ
How do I convert a US ring size to UK?
US 7 is UK N½. US 6 is UK L½. US 8 is UK P½. For a full chart, see our US to UK conversion guide.
Is a ring size 7 the same in all countries?
No. Size 7 means different things in US, UK, EU, India, and Japan. Always use inner diameter in mm as the universal reference when converting across countries.
What is the universal ring size measurement?
Inner diameter in millimeters is the most universally understood ring size measurement. It is the base for all sizing systems and works with any jeweler worldwide.
How do I convert a ring size from the UK to the US?
UK N½ is US 7. UK L½ is US 6. UK P½ is US 8. Use our UK to US conversion guide for the full chart.
