Multiply the radius times the radius. For example, if the radius of your sphere equals 19 inches, multiply 19 by 19 to get 361 square inches.
Multiply the result by the radius. In this example, multiply 361 square inches by 19 inches to get 6,859 cubic inches.
Multiply the result by 4. In this example, multiply 6,859 cubic inches by 4 to get 27,436 cubic inches.
Divide the result by 3. In this example, divide 27,436 by 3 to get 9,145.33 cubic inches.
Multiply the result by pi to find the volume of the sphere in terms of pi. In this example, multiply 9,145.33 by pi to find the volume equals 9,145.33*pi.