Ring Size Converter
Convert between US, UK, EU ring sizes, and inner diameter.
Last updated
About this tool
Diameter is the real underlying measurement — circumference is always exactly diameter × π, computed here rather than looked up, so those two numbers are always mathematically exact relative to each other. US and UK size labels come from a standard published reference chart mapping diameter to a size label; the "EU" figure shown here is the ring's circumference in millimeters, which is how the French/Swiss sizing convention actually defines a ring size (other regional systems exist and can differ by a few points, so confirm against the specific system your ring's origin uses if it matters).
Nothing you select here is sent to a server — the entire tool runs as JavaScript in your browser tab.