The solid enclosed by this surface and by two planes perpendicular to the axis is called a cylinder. A right circular cylinder is a solid described by the revolution of a rectangle about one of its sides which remains fixed. A cylinder is similar to a rectangular solid except that the base is a circle instead of a rectangle.

## Cylinder Definition

A cylinder is a 3-D geometrical shape, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. A cylinder has two parallel faces in its structure. The height of a cylinder is perpendicular to the two bases. The cylinder has a round base and a perpendicular height. Cylinder is formed by rotating one side of a rectangle about its opposite sides, keeping fixed.

Where,
r = Radius of the cylinder
h = Height of the cylinder.

## Cylinder Formulas

Let us discuss some important formulas of the cylinder:
Let the radius of the base of the cylinder be 'r' and the height be 'h'. If the cylinder is hollow then its external radius is $r_1$ and internal radius is $r_1$ and height is same as cylinder.

Important Formulae:
1. Curved surface area of cylinder = 2$\pi$rh
2. Total Surface area of the cylinder = 2$\pi$r(r + h)
3. Volume of the cylinder = $\pi r^2$h
4. Curved surface area of hollow cylinder = 2$\pi$h($r_1 + r_2$)
5. Total surface area of hollow cylinder = 2$\pi$h($r_1 + r_2$) + 2$\pi$($r_1^2 - r_2^2$)
6. Volume of hollow cylinder = $\pi$h($r_1^2 - r_2^2$).