Circumference Calculator
Calculate circle circumference, diameter and area from one positive radius in any consistent unit.
What would you like to do next?
Get three circle measures from one radius
Enter a positive radius and the calculator applies pi to show circumference, diameter and area. The shared output is convenient for geometry exercises, circular layouts, craft planning and quick checks where users know the center-to-edge distance but need the distance around the circle or its enclosed surface.
Carry the input unit through the result
The circumference and diameter use the same linear unit as the radius, while area uses the matching square unit. The page assumes a true circle and does not account for material thickness, tolerances, ellipses or paths offset from the entered radius. Measure to the correct reference line and round only as closely as the source measurement supports.
Frequently asked questions
What formula gives circumference?
Circumference equals two times pi times the radius.
How is diameter calculated?
Diameter is twice the entered radius.
What units appear in the result?
Linear outputs use the radius unit and area uses its corresponding square unit.