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📐 Solving Perimeter Problems

Perimeter is the distance all the way around a shape. Learn to add up the sides, take shortcuts for rectangles and squares, hunt down a missing side, and discover that shapes with the same perimeter c

5
lessons
~15 min
to learn
🔢 Math
subject
Adults
level
Start the course →

What you’ll learn

  1. What Is PerimeterDefine perimeter as the distance around the edge of a shape.Perimeter is the total distance all the way around the outside of a flat shape, measured in length units. Fences, frames, and borders are everyday perimeters, and every perimeter is found the same simple way.
  2. Adding Up the SidesFind a perimeter by adding the lengths of all sides.To find any perimeter, add the length of every side, going around the shape once so none is missed or double-counted. For a rectangle garden with sides 8, 5, 8, and 5, the perimeter is 26 metres.
  3. Rectangles and SquaresUse shortcuts for the perimeter of rectangles and squares.In a rectangle, opposite sides are equal, so the perimeter is two times the width plus the height. In a square all four sides are equal, so the perimeter is one side times four.
  4. Finding a Missing SideFind an unknown side length from the total perimeter.When the perimeter is known but one side is missing, add the known sides and subtract from the total; the difference is the missing side. Checking by adding all sides back to the total confirms the answer.
  5. Same Perimeter Different AreaDiscover that equal perimeters can enclose different areas.Perimeter measures the edge and area measures the space inside, so they don't always match. Two shapes with the same 12-unit perimeter can hold different areas — a 3×3 square holds 9 squares while a 1×5 strip holds only 5.

Questions this course answers

What does the perimeter of a shape measure?

Perimeter is the total distance around the outside edge of a shape — like the length of a fence around a yard.

A square has sides of 6 metres each. What is its perimeter?

All four sides are equal, so multiply one side by 4: 6 × 4 = 24 m.

A rectangle has a perimeter of 20 m. Three sides are 6 m, 4 m, and 6 m. How long is the fourth side?

The known sides add to 6 + 4 + 6 = 16. Subtract from the total: 20 − 16 = 4 m.

Two shapes both have a perimeter of 12 units. Does that mean they hold the same amount of space inside?

Perimeter measures the edge, not the space inside. A square holds more area than a long thin shape with the very same perimeter.

Grounded in trusted sources

  • Khan Academy — Perimeter (khanacademy.org)
  • Math is Fun — Perimeter (mathsisfun.com/geometry/perimeter.html)
  • BBC Bitesize — Perimeter (bbc.co.uk/bitesize)

Every Wunder lesson is built from real, reputable sources — never invented.

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