Perimeter for children

Quick answer

Perimeter is the total distance around the edge of a shape. You find it by adding up all the sides.

Learning outcome

By the end of this page, you will be able to measure the distance around any shape by adding up all its sides.

• You can identify the sides of a shape.
• You can add up all the sides to find the perimeter.
• You can measure shapes in real life and calculate their perimeter.
• You can explain how to find the perimeter of a rectangle or square.

Why this matters

Perimeter helps you understand how much space something takes up around the outside. You use it when you:

• Plan a garden or a playground
• Put up a fence around your pet's area
• Measure a room before buying a new carpet
• Build a fence or wall for a garden
• Play games like hopscotch or football on a field

Knowing how to find perimeter is useful for many things in real life, not just in maths class!

How it works

Perimeter is like walking all the way around the edge of a shape. You measure each side and add them together.

1. Look at the shape and count how many sides it has.
2. Measure each side of the shape.
3. Add up all the measurements.
4. The total is the perimeter.

For example, if you have a rectangle with sides of 5 cm, 5 cm, 3 cm, and 3 cm:

• 5 + 5 + 3 + 3 = 16 cm

The perimeter is 16 cm.

Examples you can see

Let's look at some shapes and how to find their perimeter:

Rectangle

A rectangle has 4 sides, with opposite sides equal.

Example: A rectangle is 8 cm long and 4 cm wide.

• Two sides are 8 cm each
• Two sides are 4 cm each
• Perimeter = 8 + 8 + 4 + 4 = 24 cm

Square

A square has 4 equal sides.

Example: Each side is 6 cm.

• Perimeter = 6 + 6 + 6 + 6 = 24 cm

Or, you can multiply: 6 × 4 = 24 cm

Triangle

A triangle has 3 sides.

Example: Sides are 5 cm, 7 cm, and 3 cm.

• Perimeter = 5 + 7 + 3 = 15 cm

Irregular Shape

An irregular shape has sides of different lengths.

Example: Sides are 3 cm, 4 cm, 5 cm, 2 cm, and 6 cm.

• Perimeter = 3 + 4 + 5 + 2 + 6 = 20 cm

Real-world Example: Building a Fence

Imagine you want to build a fence around your garden. Your garden is a rectangle that is 10 metres long and 5 metres wide.

• Two sides are 10 m each
• Two sides are 5 m each
• Perimeter = 10 + 10 + 5 + 5 = 30 m

You will need 30 metres of fencing to go around the garden.

Try it as a mini adventure

Adventure: Measure Your Home!

Let’s go on a perimeter adventure around your house or garden!

1. Find a rectangular room or area (like a table or a garden).
2. Measure each side with a ruler or metre stick.
3. Add up all the sides to find the perimeter.
4. Write down your measurements and the total perimeter.
5. Try with a square or a triangle shape too!

Challenge: Can you find 3 different shapes in your home and calculate their perimeter?

Common mistakes

• Mistake: Forgetting to measure all sides.
• Why it happens: It’s easy to miss one side when measuring.
• Fix: Use a pencil or finger to trace around the shape to make sure you don’t miss any side.

• Mistake: Adding the measurements incorrectly.
• Why it happens: Adding numbers can be tricky, especially with larger numbers.
• Fix: Double-check your addition or use a calculator if needed.

• Mistake: Confusing perimeter with area.
• Why it happens: Both are measurements of shapes, but one is about the edge and one is about the inside.
• Fix: Remember: perimeter = around the edge, area = inside the shape.

Parent and carer guide

Helping your child with perimeter is easy and fun!

1. Encourage your child to trace around shapes with a pencil or finger to make sure they count all sides.
2. Use real-life examples like measuring a table or a garden.
3. Let your child draw shapes and measure them with a ruler.
4. Ask questions like: "How many sides does this shape have?" or "What is the total distance around this shape?"
5. Be patient if they make mistakes – they are learning!

At home, you can also play a game where you measure different objects and find their perimeter. This helps make learning more enjoyable and memorable.

Practice questions

1. What is the perimeter of a rectangle with sides of 7 cm and 3 cm?
2. Find the perimeter of a square with sides of 5 cm.
3. A triangle has sides of 6 cm, 8 cm, and 5 cm. What is its perimeter?
4. What is the perimeter of a shape with sides 2 cm, 4 cm, 3 cm, and 5 cm?
5. A garden is 12 m long and 8 m wide. What is the perimeter of the garden?

Answers:

1. 7 + 7 + 3 + 3 = 20 cm
2. 5 + 5 + 5 + 5 = 20 cm (or 5 × 4 = 20 cm)
3. 6 + 8 + 5 = 19 cm
4. 2 + 4 + 3 + 5 = 14 cm
5. 12 + 12 + 8 + 8 = 40 m

FAQ

What is the perimeter of a shape?

The perimeter is the total distance around the edge of a shape. You find it by adding up all the sides.

How do you find the perimeter of a square?

A square has 4 equal sides. You can add them all up or multiply one side by 4.

Can you find the perimeter of any shape?

Yes! As long as you can measure all the sides, you can find the perimeter of any shape.

Why is perimeter useful?

Perimeter helps you know how much fencing, material, or space you need around a shape. It's used in building, gardening, and games.

How is perimeter different from area?

Perimeter is the distance around the edge of a shape, while area is the space inside the shape.