Area of Circle π (pi) Formula
This formula calculates the area of a circle in terms of the the geometric constant (pi). This is the traditional form of the area of circle formula, see the alternative formula in terms of the circle constant (tau).
Expression  Description 

The area of the circle.  
The geometric constant (pi), where  
The radius of the circle. 
The area of a circle is given by the constant (pi) multiplied by the radius of the circle squared. For example, to find the area of a circle with a radius of length 5 the formula is:
Substituting the value of into the formula, approximately , and evaluating the multiplication gives the area of the circle
The area of a circle with radius length is approximately units squared.
To calculate the area of a circle given a radius of one, set up the equation for the area of the circle and substitute the value of the radius into the equation.

Set up the formula and subsitute the radius in for the variable .

Evaluate the exponent expression.

Evaluate the multiplication expression.

The area of the circle is equal to units squared or approximately units squared.
To calculate the area of a circle given a radius of one, set up the equation for the area of the circle and substitute the value of the radius into the equation.

Set up the formula and subsitute the radius in for the variable .

Evaluate the exponent expression.

Evaluate the multiplication expression.

The area of the circle is equal to units squared or approximately units squared.
The greek letter π (pi) is a geometric constant approximately equal to 3.1456. The numeric value is equal to the length of any circle's circumference divided by its diameter.