**Circle Area & Circle Circumference Calculator** from radius or diameter. Our calculator computes circle circumference and area using various common units of measurement. Would you like to know the area or the circumference of a circle and the only piece of information you have is the radius or diameter of the circle? You are only one click far from the solution.

## Circle Area & Circumference Calculator

## How to use the Circle Area & Circumference Calculator?

The use of the Circle Area & Circumference Calculator is really easy: enter the diameter or the radius of the circle, the result appears immediately.

## How to calculate the circle area and circumference

### Formulas used for the calculation of a circle’s circumference and area from diameter

- The formula used for the calculation of circumference: C = d ∙ π
- The formula used for the calculation of area: A = (d/2)2 ∙ π

### The formula used for the calculation of a circle’s circumference and area from radius

- The formula used for the calculation of circumference: C = 2 ∙ r ∙ π
- The formula used for the calculation of area: A = r2 ∙ π

## What is Pi or π?

π is a mathematical constant, approximately equal to 3.1415926535. It is defined in Euclidean geometry as the ratio of a circle’s circumference to its diameter, and also has various equivalent definitions. The number appears in many formulas in all areas of mathematics and physics.