Circle Calculator

Circle Formulas

Key Formulas

Area = π × r². Circumference = 2 × π × r. Diameter = 2 × r. All formulas use π ≈ 3.14159265.

Real-World Applications

Circular calculations appear in construction (round slabs, pipes, ponds), cooking (pizza, cake tin sizing), engineering, and geometry. Knowing the circumference-to-diameter relationship is also the definition of π.

Unit Consistency

Enter all measurements in the same unit. If your radius is in metres, area will be in square metres and circumference in metres. For centimetres: area is cm², circumference is cm.