Ring Size Converter
Convert ring sizes between US, UK, EU and Japanese standards, or from diameter/circumference in mm, with a full reference chart.
About the Ring Size Converter
This ring size converter translates between the world's regional sizing standards: US/Canada numeric sizes, UK/Australia letters, EU (ISO 8653) sizes and Japanese/Chinese numbers. You can also enter an inside diameter or circumference in millimetres and it finds the nearest standard size.
Ring sizing is notoriously inconsistent between countries, which makes buying jewellery abroad or online a gamble. This tool lines up every system in one chart so you can order with confidence, whether you know your US size, a UK letter or a measurement in millimetres.
All lookups happen locally in your browser against a standard conversion chart, and the matching row is highlighted so you can see the full set of equivalents at a glance.
How to Use the Ring Size Converter
- 1Choose what you already know — a US, UK or EU size, or a measurement.
- 2Enter your value or pick your size.
- 3Read the equivalent sizes across all standards.
- 4Cross-check against the highlighted row in the chart.
Frequently Asked Questions
How do I measure my ring size at home?
Either measure the inside diameter of a ring that already fits (in mm) and enter it here, or wrap a strip of paper around your finger, mark where it overlaps, and measure that length as the circumference. Measure at the end of the day when fingers are largest, and for a warm hand.
How does US ring sizing relate to millimetres?
US sizes map to inside diameter: size 6 is about 16.5 mm, size 7 about 17.3 mm, size 8 about 18.1 mm, rising roughly 0.4 mm per half size. EU (ISO) sizes are simply the inside circumference in millimetres, so a 54 mm EU size fits a ~17.2 mm diameter.
What's my US size in UK letters?
UK and Australia use letters that step through the alphabet as the ring grows. Roughly, US 6 ≈ UK L½, US 7 ≈ UK O, US 8 ≈ UK Q, US 9 ≈ UK R½. The chart in this tool shows the exact letter for each US size.
Are ring sizes exact across brands?
Not perfectly — sizing can vary slightly between jewellers and countries, and wide bands fit tighter than thin ones. Use this converter as a reliable guide, but for an expensive ring, get sized in person or order a sizing kit when possible.
What if my measurement falls between two sizes?
The converter snaps to the nearest standard size. If you're between sizes, it's usually safer to choose the larger one, especially for wider bands or if you'll wear the ring in warm weather when fingers swell.