Number that expresses an area. This number is related to the unit of measure used.

### Formula

The area of a circle is a number that expresses the measure of the surface area of the circle.

- The formula to calculate this measure is:
*A*= π\({r^2}\) = π\(\frac{d^2}{4}\). - The letter
*A*represents the area of the circle. - The letter
*r*represents the radius of the circle. - The letter
*d*represents the diameter of the circle. - The value of π is approximately 3.1416.

### Examples

- To measure the rectangular surface area below, any of the four unconventional units of measure identified by the letters
*A*to*D*can be used.

The area of the blue rectangle is equal to 4*A*units, 8*B*units, 24*C*units or 48*D*units. - Consider the circle below with a radius of 3 cm.