To calculate the area of a semicircle, you can use the formula:

where $r$ represents the radius of the semicircle.

A semicircle is essentially half of a full circle. Therefore, to determine its area, you first need to understand the area of a complete circle. The formula for the area of a circle is:

In this formula, $\pi$ (pi) is approximately $3.14159$, and $r$ is the radius of the circle. Since a semicircle is exactly half of a circle, you simply divide the area of the full circle by $2$.

For example, if the radius of the semicircle is $4$ cm, you would first calculate the area of the full circle using the formula $\pi r^2$:

Next, to find the area of the semicircle, divide this area by $2$:

It is important to note that the radius is the distance from the center of the circle to any point on its circumference. If you are given the diameter instead—which is the distance across the circle through its center—you can find the radius by dividing the diameter by $2$. For instance, if the diameter is $10$ cm, the radius would be:

By following these steps, you can easily calculate the area of any semicircle using the formula: