Ring Size Converter
Ring sizing systems vary widely by country: the United States and Canada use a numeric scale starting around 3, the United Kingdom and Australia use letters from F to Z, continental Europe uses a numeric scale based on the inner circumference in millimetres, and the inner diameter (mm) provides a universal physical measurement. Converting between these systems is essential when buying or gifting jewellery internationally.
This converter uses a standard industry lookup table to map each US size to its UK, EU, and inner-diameter equivalents. When you enter a diameter value, the tool finds the closest matching standard size to within the nearest increment. Always verify with the jeweller if you are between sizes, as different brands may use slightly different sizing conventions.
How it works
Conversions are based on a standard lookup table derived from ISO 8653 and industry-standard ring sizing charts. EU size equals the inner circumference in mm rounded to the nearest whole number; inner diameter (mm) = EU size / π. For diameter input the nearest table entry within ±1 mm is returned.
Use cases
- Converting a US ring size to EU when buying online from a European jeweller
- Finding the UK equivalent of a ring received as a gift from abroad
- Measuring your finger diameter with a ruler and converting to US or EU size
- Resizing or ordering a custom ring from an international manufacturer
- Comparing ring sizes across different country standards when travelling