Finding the area of a circle: formula and examples

Contents

Circle is a geometric figure; the set of points on the plane that lie inside the circle.

Content

Area formula

Area of a circle (S) equals the product of the number π and the square of its radius.

S = π ⋅ r²

Circle radius (r) is a line segment connecting its center and any point on the circle.

Note: for calculations the value of a number π rounded up to 3,14.

The area of a circle is one-fourth the product of the number π and the square of its diameter:

Circle diameter (d) equals two radii (d = 2r). This is a line segment that connects two opposite points on a circle.

Task 1

Find the area of a circle with a radius of 9 cm.

Decision:

We use the formula in which the radius is involved:

S = 3,14 ⋅ (9 cm)² = 254,34 cm².

Task 2

Find the area of a circle with a diameter of 8 cm.

Decision:

We apply the formula in which the diameter appears:

S = 1/4 ⋅ 3,14 ⋅ (8 cm)² = 50,24 cm².