The formula for the area of a circle is:

A=πr2A=\pi r^2A=πr2

where AAA is the area, π\pi π (pi) is approximately 3.14, and rrr is the radius of the circle (the distance from the center of the circle to any point on its edge). This means you multiply pi by the square of the radius to get the area

. If you know the diameter ddd instead of the radius, since the diameter is twice the radius (d=2rd=2rd=2r), the formula can also be written as:

A=π(d2)2=πd24A=\pi \left(\frac{d}{2}\right)^2=\frac{\pi d^2}{4}A=π(2d​)2=4πd2​

This allows you to calculate the area directly from the diameter

. In summary:

• Using radius: A=πr2A=\pi r^2A=πr2
• Using diameter: A=πd24A=\frac{\pi d^2}{4}A=4πd2​

These formulas give the area of a circle in square units. Pi (π\pi π) is a constant representing the ratio of a circle's circumference to its diameter