Circle calculator
Area, circumference and diameter of a circle from its radius.
Area78.54
Perimeter31.42
Diameter10
Calculation formula
Area = π × r² and Circumference = 2 × π × r
Frequently asked questions
How is the circumference of a circle calculated?
The circumference equals two pi times the radius.
What if I only have the diameter?
Enter half the diameter as the radius.