Definition: The volume of a cylinder is the area of its circular base times its height, V = pi r<sup>2</sup> h, measured in cubic units.
What is the formula?
V = pi x r2 x h. Find the area of the base circle, then stack it up to the height.
How do you use it?
A can has a radius of 4 cm and height 11 cm. The base area is 3.14 x 16 = 50.24 square centimeters. Multiply by 11: 552.64 cubic centimeters.
What about cones and spheres?
A cone with the same base and height holds one third as much: V = (1/3) pi r2 h, here about 184.21. A sphere has V = (4/3) pi r3. For r = 3, V = (4/3)(3.14)(27) = 113.04.
How do you go backward?
A cylinder holds 785 cubic inches and has height 10. Then pi r2 = 78.5, so r2 = 25 and r = 5 inches.
What are common mistakes?
Using the diameter instead of the radius, or forgetting to square the radius. Another is to give square units for volume. Volume always uses cubic units.