A circle is a round shape with each point equally far from the centre. When finding the area of a semicircle, the easiest way to proceed is to find the area of a full circle and divide by two, because a semicircle equals half of a full circle. You might need to know the area of a semicircle if you are painting a design or a sign and you need to know the size of the area you need to cover.
Measure the distance from one side of the circle to the other, passing through the circle centre. This is the diameter.
Divide the diameter by 2 to find the radius of the semicircle. For example, if you have a diameter of 14 inches, you would divide 14 by 2 to get 7 inches.
Square the radius. In this example, the radius equals 7 inches, so you would multiply 7 inches by 7 inches to get 49 square inches.
Multiply the answer in Step 3 answer by 3.14 (the value of pi) to find the area of a full circle. In this example, you would multiply 49 square inches by 3.14 to get 153.86 square inches.
Divide the area of the full circle by 2 to find the area of the semicircle. Completing the example, you would divide 153.86 square inches by 2 to find that the area of the semicircle equals 76.93 square inches.