To find the area of a semicircle, find the area of the full circle, then divide by two. See Step 1 for a quick way to find the area of a semicircle.
Step
Step 1. Find the radius of the semicircle
The value of the radius is needed to find the area of a semicircle. Let's say the radius of the semicircle is 5 cm.
If all you know is the diameter of the circle, divide by two to get the radius. For example, the diameter of a circle is 10 cm, so 10 divided by 2 (10/2) is 5 cm for the radius
Step 2. Find the area of the full circle and divide by two
The formula for finding the area of a full circle is r2, it is known that "r" is the radius of the circle. Since our goal is to find the area of a semicircle, the result obtained after using the formula is divided by two. So, the formula for the area of a semicircle is r2/2. Now plug "5 cm" into the formula. We can use the closest approximation to with a calculator, replacing with 3, 14, or just leave. Here's how to do it:
- Area = (πr2)/2
- Area = (π x 5 cm x 5 cm)/2
- Area = (π x 25 cm2)/2
- Area = (3, 14 x 25 cm2)/2
- Area = 39.25 cm2
Step 3. Remember to always state your answer in square units
Since what you are looking for is the area of a shape, what is used in the answer is square units (e.g. cm2) to denote a two-dimensional object. If volume is calculated, use cubic units (eg cm3).
Tips
- The area of a circle is (pi)(r^2).
- The area of a semicircle is (1/2)(pi)(r^2).
