Ring Size Converter
Convert ring size between US, EU, UK and inner circumference in millimeters.
Results
What is it?
The Ring Size Converter translates a finger's inner circumference (measured in millimeters) into the major international ring-size systems: US (numerical, half sizes), EU (ISO 8653 standard, circumference minus 40), UK (alphabetical — this calculator shows a numeric proxy), and inner diameter in mm.
How to use
Cut a thin strip of paper about 10 cm long. Wrap it around the base of your finger, mark where the paper overlaps, and measure that length with a ruler in millimeters. Enter the millimeter value into the calculator.
Example scenario
Inner circumference measured as 57 mm: US size approximately 8, EU size = 17, inner diameter approximately 18.15 mm. This is one of the most common ring sizes sold.
Pro tip
Fingers swell throughout the day — they are smallest in the morning and largest in the evening after activity. Measure in the evening for the most comfortable everyday fit. For a ring that will be worn all the time, measure when your hands are warm (not cold). Different metals have different comfort profiles: wider bands feel tighter, so size up half a size for bands wider than 6 mm.