Finding the Volume of a Semicircle

Because a semicircle is a two-dimensional shape, it has an area rather than volume. You might need to know the area of a semicircle if you want to paint a semicircular area or if you want to lay sod in a semicircular area. To find the area of a semicircle, you need to know the diameter, which is the distance across the semicircle. If you have half a sphere, you can find the volume by finding the area of the whole sphere and dividing by 2.

Semi-Circle Area

Step 1

Measure the distance across the semicircle to find the diameter of the semicircle.

Step 2

Divide the diameter by 2 to find the radius. For example, if the semicircle diameter equals 14 inches, divide 14 by 2 to get a radius of 7 inches.

Step 3

Square the radius. In this example, square 7 to get 49.

Step 4

Multiply the squared radius by 3.14 to get 153.86 square inches.

Step 5

Divide 153.86 by 2 to find the area of the semicircle. Completing the example, divide 153.86 by 2 to get 76.93 square inches.

Hemisphere Volume

Step 1

Measure the distance across the bottom of the hemisphere to find the diameter.

Step 2

Divide the diameter by 2 to find the radius. For example, if the hemisphere diameter equals 14 inches, divide 14 by 2 to get a radius of 7 inches.

Step 3

Cube the radius. Cubing means to multiply the number by itself three times. In this example, multiply 7 times 7 times 7 to get 343 cubic inches.

Step 4

Multiply the previous result by 4/3. In this example, multiply 343 by 4/3 to get 457.33 cubic inches.

Step 5

Multiply the previous result by 3.14 to find the volume if you had a full sphere. In this example, multiply 457.33 by 3.14 to get 1,436.03 cubic inches.

Step 6

Divide the volume of the full sphere by 2 to find the volume of the hemisphere. In this example, divide 1,436.03 by 2 to get 718.02 cubic inches.

Things Needed

• Measuring tape
• Calculator