A drum head is in the shape of a circle.
To find the area of a circle, use this formula:
Area of a circle = π r²
π or pi is equal to 3.14159265359. But to lessen confusion and ensure uniformity, π is equal to 3.14.
r is the radius of the circle. radius is the line from the center of the circle to the edge of the circle. you have to raise the radius to the 2nd power.
For example:
radius is 3 cm
Area of a circle = 3.14 * (3cm)²
= 3.14 * 9cm²
Area of a circle = 28.26 cm²