Area of Circle Formula
The area of a circle is given by mutiplied by the circle constant (tau) multiplied by the radius of the circle squared.
Expression  Description 

The area of the circle.  
The circle constant (tau), where  
The radius of the circle. 
The area of a circle is given by mutiplied by the circle constant (tau) 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:
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.

Substitute the length of the radius into the formula.

Evaluate the exponent expression and simplify.

Substitute the value of into the expression.

Evaluate the multiplication.

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

Substitute the length of the radius into the formula.

Evaluate the exponent expression and simplify.

Simplify the fraction.

Substitute the value of into the expression.

Evaluate the multiplication.

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

Substitute the length of the radius into the formula.

Evaluate the exponent expression and simplify.

Substitute the value of into the expression.

Multiply the fraction by the value of .

The area of a circle of radius is approximately units squared.
The circle constant τ (tau) is a geometric constant approximately equal to 6.283. The numeric value is defined as the length of any circle's circumference divided by the length of its radius.