Perimeter: Rectangles and Squares (KS2)

ME8Perimeter

The distance all the way round.

Perimeter is the total distance around the outside of a shape.

Walk around the rectangle.

8 + 5 + 8 + 5 = 26 cm

Rectangle shortcut: P = 2 × (length + width)

Learn the 3-Step Method

1Add every side.

Perimeter = walk around the whole edge, adding as you go.

8+5+8+5

2Use the rectangle shortcut.

Opposite sides are equal: P = 2 × (8 + 5) = 26.

2 × 13 = 26

3Regular shapes: multiply.

A square's four equal sides: P = 4 × side. Equilateral triangle: 3 × side.

4 × 6 = 24

💡 Key IdeaPerimeter is a length — answer in cm, m or km, never cm².

Worked Example

A rectangular garden is 12 m long and 7 m wide. How much fencing is needed?

Add the pair

12 + 7 = 19

→

Double it

2 × 19 = 38

→

✓ Answer

38 m of fencing

Watch Out! Common Mistakes

Only adding two sides.

P = 8 + 5 = 13 cm ✕

Wrong! Go all the way round — four sides: 8+5+8+5 = 26 cm.

Confusing perimeter with area.

P = 8 × 5 = 40 cm ✕

Wrong! Multiplying gives area (40 cm²). Perimeter ADDS the sides: 26 cm.

Missing hidden sides.

Careful with L-shapes! Every edge counts, including the ones inside the notch. Label every side before adding.

⬇ Cheat Sheet

PERIMETER

Perimeter = total distance around the outside.
Rectangle: P = 2 × (length + width).
Square: P = 4 × side.
Answer in length units (cm, m) — never cm².

Examples: 8×5 rectangle → P = 26 cm · 12×7 garden → 38 m

📖 Continue Your Journey

✓ ME1 Units of Length ✓ ME2 Converting Length ✓ ME3 Units of Mass ✓ ME4 Converting Mass ✓ ME5 Units of Capacity ✓ ME6 Converting Capacity ✓ ME7 Reading Scales ME8 Perimeter ME9 Area of Rectangles ME10 Area of Triangles ME11 Area of Parallelograms ME12 Compound Shapes ME13 Volume of Cuboids ME14 Telling the Time ME15 Time Calculations ME16 Money Calculations ME17 Imperial and Metric Units ME18 Measurement Problem Solving

→

Next Lesson: ME9 Area of RectanglesCount the squares inside — or multiply.

📄 Free printable: Download the Perimeter cheat sheet (PDF) — keep it by your child's desk.

Quick summary

Perimeter is the total distance around the outside of a shape.
Rectangle shortcut: P = 2 × (length + width).
Square: P = 4 × side.
Perimeter is a length (cm, m) — multiplying sides gives area instead.

Frequently asked questions

What is perimeter?

The total distance around the outside edge of a shape — like the fencing needed to go round a garden.

What is the formula for the perimeter of a rectangle?

P = 2 × (length + width). A 12 m by 7 m garden needs 2 × 19 = 38 m of fencing.

How is perimeter different from area?

Perimeter measures around the edge (in cm or m); area measures the surface inside (in cm² or m²). Adding sides gives perimeter; multiplying them gives area.

ME9 Area of Rectangles