Circle Calculator
Calculate the area, circumference, and diameter of a circle from its radius.
GeometryFree · no sign-upStep-by-step answers
How to use this calculator
- 1Enter your values or expression in the fields above.
- 2Press Enter or click the calculate button.
- 3Read the result, then follow the numbered step-by-step working to understand each stage.
Worked Examples
Frequently Asked Questions
What is π?
π (pi) ≈ 3.14159 is the ratio of a circle's circumference to its diameter.
Related Calculators
Learn the concepts
Understand the theory behind this calculator.
Geometry
Circles
A circle is the set of points equidistant from a center point. It is defined by its radius or diameter.
Geometry
Area
Area measures the amount of space inside a two-dimensional shape.
Geometry
Angles
An angle is formed by two rays sharing a common endpoint. Angles are measured in degrees or radians.
Geometry
Triangles
A triangle is a polygon with three sides. The angles sum to 180°.