Last updated: November 19, 2025
Circle circumference calculator explained
Circumference is the distance around a circle. This calculator uses and to convert any radius, diameter, or circumference value into the others, making it easy to plan circular gardens, wheels, or pipes without redoing the algebra.
How the conversion works
The formulas come directly from the definition of :
Because diameter , both expressions are equivalent. The calculator solves for whichever variable is missing, and it can surface decimal or symbolic multiples of depending on your needs.
Units and conversions
| Quantity | Units | Notes |
|---|---|---|
| Radius | cm, m, in, ft | Converts to meters internally. |
| Diameter | same as radius | Always twice the radius. |
| Circumference | same | Output uses the same unit you chose for inputs. |
Worked examples
- Wheel circumference
Bicycle wheel radius 0.34 m:
One rotation moves the bike 2.14 m down the road.
- Pipe diameter from perimeter
Need 3 m of trim to wrap a circular table, so m.
Tips and pitfalls
- Use consistent units; if radius is in inches, circumference will be too.
- Report exact answers like when working in algebra class; use decimals for construction projects.
- To find area from circumference, compute then .
- When measuring a physical object, wrap a tape measure around it to capture circumference directly, then convert to radius or diameter.