Ring Size Calculator
NewConvert a finger circumference or ring inner diameter measurement (in mm) into US, UK/AU, and EU ring sizes using a standard sizing reference table.
—
US ring size
UK/AU size
EU size
Diameter (mm)
Frequently Asked Questions
How do I measure finger circumference at home?
Wrap a strip of paper or string snugly around the base of your finger, mark where it overlaps, then measure that length in millimeters with a ruler — that measurement is your finger circumference, which you can enter directly into this calculator.
What's the difference between circumference and diameter measurements?
Circumference is the distance around your finger; diameter is the distance straight across an existing ring's inner opening. If you're measuring an existing ring that fits well, select "Ring inner diameter" instead of circumference, since diameter = circumference ÷ π and using the wrong option would give an incorrect size.
Why do US, UK, and EU sizes use different numbering systems?
Each region historically developed its own ring-sizing convention — the US/Canada system uses a numeric half-size scale, the UK/Australia system uses letters (A through Z and beyond), and most of continental Europe measures the actual inner circumference in millimeters directly as the "size" number — none of these map to each other with a simple formula, which is why a reference conversion table is needed.
Why might my actual ring size differ slightly from this estimate?
Ring width, metal type, and finger shape all affect fit — wider band styles typically need a slightly larger size than thin bands for the same finger, and finger size itself can fluctuate with temperature, time of day, and swelling. Getting professionally sized in person at a jeweler is the most reliable method for an important purchase.