Calculate the Surface Area of a Prism - dummies

Calculate the Surface Area of a Prism

By Mark Ryan

Because prisms have two congruent bases, it’s easy to calculate their surface area: first, you find the area of one base and double that value; then, you add the prism’s lateral area.

The lateral area of a prism is the area of its sides—namely, the area of everything but the prism’s bases. Although the bases of a prism can be any shape, the lateral area is always made up of rectangles. So to get the lateral area, all you need to do is find the area of each rectangle (using the standard rectangle area formula) and then add up these areas.

A prism with its bases and lateral rectangles.

You can use this formula to find the surface area of a prism:


Now, here’s an example.


Here’s the proof diagram.


You have everything you need to compute the surface area. Just plug in the numbers: