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Ring Size Calculator
Enter your finger circumference to get your US ring size and diameter.
US ring size
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From circumference.
| Inside diameter | — |
|---|---|
| Circumference | — |
| UK size (approx) | — |
| — |
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Enter your figures above to see the step-by-step working.
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How the Ring Size Calculator Works
US ring sizes are based on the inside diameter of the band. Measure around the finger to get its circumference in millimetres, divide by π to get the diameter, and convert: each US whole size is 0.8128 mm of diameter, starting from 11.63 mm at size 0. Wrap a strip of paper around your finger, mark where it overlaps, and measure the length for the circumference.
Measure at the end of the day when fingers are largest, and size up slightly for wide bands. The calculator also gives an approximate UK letter size.
US size = (circumference ÷ π − 11.63) ÷ 0.8128
Frequently Asked Questions
How do I measure my ring size at home?
Wrap a strip of paper or string around the base of your finger, mark the overlap, and measure that length in millimetres. Enter it as the circumference.
What is a common ring size?
US size 6–7 is typical for women and 9–10 for men, but it varies widely. Measure to be sure.
When should I measure?
At the end of the day and when warm — fingers shrink when cold and are smallest in the morning.
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