US to EU Ring Size Converter
Convert ring sizes between the US, UK, EU/ISO and Japanese systems, or start from a measured diameter or circumference in millimetres.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
This page opens the ring size converter with the direction already set: from the US & Canada scale to the European ISO size. Type an American size such as 7 or 6.5, press the button, and you get the EU size — which is simply the inner circumference in millimetres — together with the matching UK letter, Japanese size and inner diameter.
The two scales are built differently: US sizes grow in quarter and half steps of about 0.8 mm of diameter per full size, while the EU/ISO 8653 size is the circumference itself, so a US 7 corresponds to roughly EU 54.4 and a US 6 to about EU 52. Because the systems do not align on round numbers, a conversion table beats mental math every time.
This direction is most useful when you know a size from an American brand and want to order from a European jeweller. If the result lands between two European sizes in the shop's catalogue, take the larger one — a slightly loose ring can be worn, a tight one cannot.
Example. US size 7 maps to inner diameter 17.32 mm, circumference 54.4 mm, UK N½, and Japanese size 14.
Limit. Circumferences outside the published table, roughly the span around US sizes covered by the ISO rows, are rejected.