Prisms are polyhendric geometric forms that come in several forms — that means that they are solid and exist in three dimensions. It also means that their surface area is flat — unlike a sphere — and that they are marked by straight edges, like a square or rectangle. Finding the perimeter of a prism is fairly easy to do and requires only several basic calculations.
Find a prism. If using an actual prism, place the object on a flat surface. Or, if using an image of a prism, determine whether the image represents the true proportion of the object or a ratio.
Measure the length of each of the sides of the base. Types of prisms vary — hexagonal, triangular, pentagonal, for instance. So, with some prisms you will have more measurements to make than with others.
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Add the measurements of each side of the base. The resulting figure is the total length of the perimeter of the prism. For instance, if the three sides of a triangular prism measure one, two and three inches, the perimeter of the prism will be six inches.