Ring Size International Converter

About this calculator

Ring sizes aren't standardized globally — the US/Canada system uses a numeric scale (roughly 3 to 13, often with half sizes), the UK/Australia system uses letters (A through Z+), the EU/ISO system uses the finger's inner circumference directly in millimeters, and Japan uses its own numbered scale — and all four ultimately trace back to the same underlying physical measurement: the ring's inner circumference (or equivalently, inner diameter), since that's what actually determines fit regardless of which country's chart you're reading.

This calculator lets you pick your known sizing system and a size, then converts it to the equivalent size in the other three systems via that shared circumference/diameter measurement. Online jewelry shoppers ordering from an overseas retailer, jewelers fulfilling international orders, and people buying a ring as a gift while traveling abroad use it to avoid ordering the wrong size when a size "7" in the US doesn't mean anything in a UK or Japanese size chart.