Circle Calculator

How this circle calculator works

Enter the radius of a circle. The calculator instantly shows the diameter, circumference, and area.

Circle formulas

• Diameter = 2 × radius
• Circumference = 2 × π × radius
• Area = π × radius²

About π (pi)

π ≈ 3.14159265358979... It is the ratio of a circle's circumference to its diameter. This calculator uses JavaScript's Math.PI constant for maximum precision (about 16 significant digits).