Math Calculators

Circle Calculator

Calculate the area, circumference and diameter of a circle from its radius, in the unit of your choice.

Area —

Circumference —

Diameter —

About the Circle Calculator

Given a circle's radius, you can find its area, circumference and diameter using the constant π (approximately 3.14159). The radius has its own unit selector, and so does each result — pick centimeters for your input and square feet for your area if that's what you need, and the calculator converts everything automatically.

Formulas: Area = πr² · Circumference = 2πr · Diameter = 2r

These are the foundational formulas for working with circular shapes in geometry, engineering and design.