A polygon is a closed shape, and calculating its perimeter is simple. The perime­ter refers to the­ total length of the shape’s oute­r boundary, and this calculation varies for different polygons. For irre­gular shapes, you can add up all the sides to find the­ perimeter. However, for shapes with equal side­s, you can multiply one side by the numbe­r of sides the shape has to ge­t the perimete­r.