Enter either the circumference or diameter (any length unit), then click calculate to get the other value.
This tool is based on the circle circumference formula C = πd, where C is circumference and d is diameter, with π approximately 3.14159.
If you know the circumference, you can get the diameter with d = C ÷ π. If you know the diameter, you can calculate the circumference using C = π × d.
As long as you use the same length unit for both values, this calculator works for classroom geometry, layout design, mechanical parts and more.
Make sure the input is greater than zero. For higher precision, you can keep more decimal places or use the result as part of further calculations.
C = πd, or equivalently C = 2πr.
Diameter d = 2r.
Enter the diameter in its box, leave the circumference empty, and click calculate.
Enter the circumference, leave the diameter empty, and click calculate to get d = C ÷ π.
Because the formula links the two directly; one known value is enough to compute the other.
Yes. Circumference and diameter must use the same unit, such as all in cm or all in mm.
For most work, 3.14 is fine; for higher precision, use 3.1416 or more digits.
Circumference is the length around the circle; area measures how much space the circle covers.
Students, teachers, designers and engineers who need quick circle size conversions.
It is faster, avoids arithmetic errors and allows rapid comparison of multiple inputs.
Quickly convert between circle circumference and diameter. Useful for study, design and engineering.
Scan the QR code to use this tool on mobile.