Ring Diameter to Circumference Converter
Enter an inner diameter measurement and instantly get the circumference, radius, and matching ring size — no need to work out the math yourself.
Diameter, circumference, and radius converter
Enter any one of the three and we'll work out the other two, plus the matching ring size.
The diameter-to-circumference formula
This is a fixed geometric relationship, not a ring-sizing rule.
For any circle, circumference = diameter × π (pi, approximately 3.1416). A ring's inner diameter and inner circumference describe the exact same size — they're just two different ways of measuring the same circle, and one always determines the other precisely.
Why you might need this
- You measured a ring's inside diameter but a chart or supplier asks for circumference.
- You're comparing two rings measured in different ways.
- You just want the underlying geometry, separate from a specific sizing system.
Frequently asked questions
How do I convert ring diameter to circumference?
Circumference is always diameter × π (about 3.1416) — enter your inner diameter measurement above in mm, cm, or inches and the circumference is calculated instantly, along with your matching ring size.
Where do I measure a ring’s diameter?
Lay the ring flat and measure straight across the inside of the band, from one inner edge to the other — not the outside of the band, which includes the metal’s thickness and reads larger than the true size.
Why does this tool also show a ring size?
Since your inner diameter already tells us your ring size, we show it as a bonus alongside the pure geometry conversion — no extra input needed.