By what number do you need to multiply the volume of the cone to get the volume of the cylinder?

You need to multiply the volume of a cone by 3 to get the volume of its corresponding cylinder (a cylinder with the same base radius and perpendicular height).

As in:

Vol. of a cylinder = πr²h

and Vol. of a cone = ⅓πr²h

So assuming volume of a cone is ⅓V, then the volume of the cylinder will be ⅓V * 3 which equals V.