The volume of the cylinder is
V = pi r^2 h
where:
r : radius of cross section.
pi: const = 3.14
h: height of the cylinder
You can think of it in terms of a circle which you keep cloning to create the height so each time you gain the same circle area.
The formula can be proved using integration. (if you want request).
h = 5m
r = D/2 = 10/2 = 5 m
Pi = 3.14
V = 3.14 (5)^2 * 5 = 392.5 m^3
