Find Your Ring Size from a Radius Measurement
Ring sizing charts are published in diameter or circumference, never radius — enter your radius here and we'll do the conversion for you.
Diameter, circumference, and radius converter
Enter any one of the three and we'll work out the other two, plus the matching ring size.
Radius is simply half the diameter
This is a fixed geometric relationship, not a ring-sizing rule.
A circle's radius is the distance from its center to its edge — exactly half the diameter. Since every published ring-sizing standard is defined by inner diameter or inner circumference, this tool doubles your radius value first, then looks up the result the same way "I have a ring that fits" mode does on the main calculator.
Why you might have a radius instead
- Some calipers and mandrels report radius directly rather than diameter.
- Jewelry design and CAD tools sometimes specify inner radius, not diameter.
- If you already have a diameter or circumference measurement instead, use the main ring size calculator directly.
Frequently asked questions
What is a ring’s radius, and how is it different from diameter?
Radius is the distance from the center of the ring’s inner circle to its edge — exactly half the inner diameter. Ring sizing charts are published in diameter or circumference, never radius, so this tool doubles your radius value first and then looks up the matching size.
Why would I have a radius measurement instead of a diameter?
Some calipers, mandrels, and jewelry design tools report radius directly rather than diameter — if that’s what you have on hand, enter it here instead of doubling it yourself.
Is converting radius to diameter exact?
Yes — doubling a radius to get a diameter is a fixed mathematical relationship with no room for error. Any uncertainty in your result comes only from how precisely the radius itself was measured.