How to use Ring Size Converter
Select your US ring size to see the matching UK letter, EU/ISO number, and inside diameter and circumference in millimetres.
Frequently asked questions
How is ring size measured?
Ring size is set by the inside circumference; EU/ISO size equals that circumference in millimetres.
How do diameter and circumference relate?
circumference ≈ diameter × π, so a wider band means a larger circumference and size.
Are half sizes exact?
Half sizes and letter grades vary slightly by brand, so treat the chart as a close reference.
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