How to Find the Perimeter of an Eight-Sided Shape

Use formulas, given information or a ruler to find the perimeter of eight-sided shapes.

Geometric shapes, or polygons, consist of a closed plane figure. The perimeter of geometric shapes is equal to the lengths of all the sides that make up the shape. The sides may exist in equal or varying lengths. If you need to know the perimeter of an eight-sided shape, you can use information that you already have about the eight-sided shape and calculate the perimeter on your own. Alternatively, you can measure the perimeter by hand.

Instructions

1. Work the formula P = n x s, if the eight-sided shape is a regular polygon, which means that all sides and angles are equal. P = perimeter, n = number of sides and s = the length of one side.

2. Apply the P = A + B + C + D + E + F + G + H if the eight-sided shape is irregular. Irregular means that the shape does not have equal sides and angles. P = perimeter and alphabets A through H represent sides of the eight-sided shape.

3. Measure each side of the eight-sided shape if you have the shape on hand. Add up all the sides to find the perimeter.

Tips & Warnings

• If not all eight sides are equal and you only know the length of some of the sides, use area formulas to help you find the lengths of the unknown sides. If you know the area you may be able to partition the polygon into other shapes, for example rectangles (base x height) and triangles (1/2 base x height) and work from there.

References

• Web Formulas: Perimeter of a Polygon