Ring Size converter
US sizes, inner circumference and diameter.
Ring sizes are all derived from the inner circumference of the band. The US scale adds about 2.55 mm of circumference per size, the ISO standard quotes the circumference in millimetres directly, and France and Spain quote the circumference minus 40. Measure a ring that already fits rather than your finger, at room temperature.
Result
1 US = 39.0905 mm
Multiply by 2.5535, then + 36.537.
Fingers change size with temperature and time of day, and wide bands fit tighter. Have a jeweller confirm before buying. About accuracy
All ring size units
Inner Circumference (mm)mm
US / Canada SizeUS
Inner Diameter (mm)mm Ø
France / Spain SizeFR
Inner Diameter (inches)in Ø
Inner Circumference (inches)in