Volume of Cylinders, Cones and Spheres for Kids: Formulas with Pi (Grade 8 Math)

Hi, I'm Luna from DoodleBeez. Today we are learning how to find the volume of cylinders, cones and spheres. Volume is the space inside a solid. All three shapes use pi and the radius, and we will use three point one four for pi.

A cylinder is like a can. Its base is a circle, and the area of a circle is pi times the radius squared. Multiply that by the height to get the volume. V equals pi r squared h.

Let's try one. A cylinder has a radius of three centimeters and a height of ten centimeters. Three squared is nine, and nine times ten is ninety. So the volume is ninety pi, about two hundred eighty two point six cubic centimeters.

A cone with the same base and height holds exactly one third of the cylinder. So V equals one third pi r squared h. Our cone would hold ninety pi divided by three, which is thirty pi, about ninety four point two cubic centimeters.

A sphere is a ball. Its volume is four thirds pi r cubed. For a radius of three centimeters, three cubed is twenty seven, and four thirds of twenty seven is thirty six. That is thirty six pi, about one hundred thirteen cubic centimeters.

Two quick tips. If a question gives the diameter, halve it first to find the radius. A diameter of eight centimeters means a radius of four. And always write volume in cubic units, like cubic centimeters.

Now it's your turn. A cone has a radius of three and a height of four centimeters. Find its volume. Pause and try. Nine times four is thirty six, and one third is twelve. That is twelve pi, about thirty seven point seven cubic centimeters.

Great job! Remember, a cylinder is pi r squared h, a cone is one third of that, and a sphere is four thirds pi r cubed. Practice volume of cylinders, cones and spheres in Middle School Math at doodlebeez.com. See you next time!