# area of a circle

## Calculus area_circle

area online calculator that can calculate the area of a circle from its radius or from its diameter.
area_circle(3) returns 9pi

### Function : area_circle

#### Summary :

area online calculator that can calculate the area of a circle from its radius or from its diameter.

area_circle online

# Area circle calculator

The calculator has several features allowing it to make surface calculations. It is thus possible to calculate the surface of a circle, also called area of a disc through area_circle function, but also the surface of a rectangle , or the surface of a square (which is a particular rectangle).

Calculating the area of a circle can be done from its radius or its diameter.

## Calculating the area of a circle from its radius

The area of a circle is the area bounded by the circle. The area of a circle is given by the formula pi*r^2 where r represents the radius of the circle.

Thus, calculating the area of a circle with radius 3 is done by typing the following formula area_circle(3) , after calculation, the result 9pi is returned.

It is also possible to make symbolic calculation and calculate the area of a circle with radius 1+x, by typing the following formula area_circle(1+x) , after calculation, the result is returned.

## Calculating the area of a circle from its diameter

If d is the diameter of the circle and its radius r, then the radius of a circle is equal to half of its diameter which is expressed by the formula r=d/2. From this formula, it is possible to determine the area of a circle from its diameter.

The area of a circle can be calculated from its diameter using the formula pi*(d/2)^2, where d is the diameter of the circle.

Thus, calculating the area of circle with diameter 5 is done by entering the following formula area_circle(5/2) , after calculation, the result 25/4*pi is returned.

## Games and quizzes on calculating the areas of common geometric figures

To apply the different calculation formulas, several quizzes on the calculation of the area of the square, the rectangle, and the circle are proposed.

area online calculator that can calculate the area of a circle from its radius or from its diameter.

#### Syntax :

area_circle(3) returns 9pi