How to find a ring size
Measure the finger, then compare US and EU sizing.
1
Measure the finger
Use a paper strip or ring sizer around the base of the finger.
2
Enter millimetres
Use the marked length as the circumference.
3
Check both systems
Use the US and EU rows to match the jeweller size chart.
What does this tool do?
Ring size is based on the inner diameter, which follows directly from the finger circumference. This calculator converts a millimetre measurement into US half sizes and the ISO European size.
The Formula
Diameter = circumference ÷ π; US size ≈ (diameter − 11.63) ÷ 0.8128; EU size = circumference − 40Frequently Asked Questions
How do I measure a finger?
Wrap a strip of paper around the base of the finger, mark the overlap, and measure the length in millimetres against a ruler. Measure the exact finger that will wear the ring.
Does ring width matter?
Yes. Wide bands fit tighter, so many jewellers suggest going up a half size for a band wider than about six millimetres.