Math

you need to know the height for both of the formula's

The formula for the volume a cylinder is pi(r^2)h.

The formula of the volume of a rectangular prism is l(h)(w).

In both, you are multiplying the base by the height.

Cylinder:

You take the surface area of the circle and multiply it by the height.

Rectangular Prism:

You take the surface area of the base (rectangle/square) and multiply it by the height.