Perimeter of Composite Figures

Perimeter of Composite Figures

A composite figure is made by joining simpler shapes. To find its perimeter, focus on the outside edges only. Any side hidden inside the shape does not count.

1) Trace the boundary

Go around the outside of the figure and list every edge that belongs to the perimeter. If a side is split into smaller segments, add all those visible parts.

2) Ignore interior sides

If two shapes are joined along a common side, that shared side is inside the figure. Do not include it in the perimeter.

3) Add the side lengths

Write the lengths of all outer sides and add them carefully. If the expression has like terms, combine them before writing the final simplified answer.

4) Keep units and simplify

Your answer should be a single perimeter value with units, such as cm, m, or in. Simplify any algebraic expression if the problem uses variables.

Quick check

• Did you count only the outside boundary?
• Did you leave out shared interior edges?
• Did you include every visible side exactly once?

If you are unsure, mark each perimeter edge with a finger or pencil as you move around the shape. This helps avoid missing a side or counting one twice.