Geometry For Dummies, 3rd Edition
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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.

geometry-prism
A prism with its bases and lateral rectangles.

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

geometry-area

Now, here's an example.

geometry-area-example

Here's the proof diagram.

geometry-prism-diagram

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

geometry-area-prism

About This Article

This article is from the book:

About the book author:

Mark Ryan is the founder and owner of The Math Center in the Chicago area, where he provides tutoring in all math subjects as well as test preparation. Mark is the author of Calculus For Dummies, Calculus Workbook For Dummies, and Geometry Workbook For Dummies.

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