Castle maths quest: perimeter
A story-led junior maths adventure using towers, walls and dragon-proof designs to measure fences, walls and safe zones around places.
Quick answer
Perimeter is the total distance around the edge of a shape. You can find it by adding up all the sides of a shape, like walking around the outside of a castle wall or measuring how far you need to go to fence in a dragon-proof garden.
Learning outcome
By the end of this page, you will be able to measure the perimeter of any shape by adding up all its sides.
- You can walk around any shape and count how far you go all the way around
- You can add up all the sides of a shape to find the perimeter
- You can measure shapes using a ruler or by counting steps
- You can help build a safe castle by working out how much fencing you need
Why this matters
Perimeter helps you know how much fencing you need for a garden, how far you run around a playground, or how long a wall needs to be to keep dragons out of your castle. It's useful for planning and building things safely and smartly. When you know perimeter, you can make sure you have enough materials for your projects!
How it works
Perimeter is like taking a walk around the outside of any shape. Here's how to find it:
- Look at all the sides of the shape
- Measure each side (or count the steps)
- Add all the sides together
- The total is the perimeter
It doesn't matter if the shape is a square, rectangle, triangle, or even a castle tower – you just count how far you walk around the outside!
Examples you can see
Let's imagine you're building a dragon-proof castle. You want to know how much fencing you need for your garden wall.
Example 1: Square garden
Your garden is a square with sides of 5 metres each.
| Side | Length |
|---|---|
| Side 1 | 5 metres |
| Side 2 | 5 metres |
| Side 3 | 5 metres |
| Side 4 | 5 metres |
Perimeter = 5 + 5 + 5 + 5 = 20 metres
Example 2: Rectangular tower
Your tower is 8 metres wide and 6 metres tall.
| Side | Length |
|---|---|
| Side 1 | 8 metres |
| Side 2 | 6 metres |
| Side 3 | 8 metres |
| Side 4 | 6 metres |
Perimeter = 8 + 6 + 8 + 6 = 28 metres
Example 3: Triangle wall
Your wall is a triangle with sides of 4, 5, and 3 metres.
| Side | Length |
|---|---|
| Side 1 | 4 metres |
| Side 2 | 5 metres |
| Side 3 | 3 metres |
Perimeter = 4 + 5 + 3 = 12 metres
Try it as a mini adventure
Castle Perimeter Quest
You are the castle architect and your mission is to plan the perfect dragon-proof wall around the castle garden. You have three shapes to measure:
- First, you need to measure a square garden with sides of 7 metres
- Then, a rectangular tower that is 10 metres wide and 5 metres tall
- Finally, a triangular wall that is 6, 8, and 10 metres long
How much fencing do you need for each shape?
Step 1: Square garden with sides of 7 metres
Perimeter = 7 + 7 + 7 + 7 = 28 metres
Step 2: Rectangular tower 10 metres wide and 5 metres tall
Perimeter = 10 + 5 + 10 + 5 = 30 metres
Step 3: Triangular wall 6, 8, and 10 metres
Perimeter = 6 + 8 + 10 = 24 metres
Total fencing needed: 28 + 30 + 24 = 82 metres
You have enough time to build a safe castle with the right amount of fencing!
Common mistakes
- Mistake: Forgetting to measure all sides of a shape
- Why it happens: When you're walking around a shape, you might miss one side if you're not careful
- Fix: Use your finger to trace around the shape and count each side once
- Mistake: Adding the length and width instead of all sides
- Why it happens: You might think of area instead of perimeter
- Fix: Remember: perimeter = walk around the outside, so add all sides
- Mistake: Confusing metres with centimetres
- Why it happens: Sometimes it's hard to tell which unit you're using
- Fix: Always check that all measurements are in the same unit before adding
Parent and carer guide
Help your child practice perimeter by:
- Measuring the sides of a room or table with a ruler or tape measure
- Walking around shapes together and counting the sides
- Using everyday objects like books, boxes, or toys to make shapes
- Playing a game where you ask, "How far would you walk around this shape?"
- Building with blocks and calculating how much fencing you'd need for a wall
Don't worry if they make mistakes – they're learning! Encourage them to check their work and explain their thinking.
Practice questions
- What is the perimeter of a square with sides of 4 metres?
- What is the perimeter of a rectangle that is 6 metres wide and 3 metres tall?
- What is the perimeter of a triangle with sides of 5, 7, and 8 metres?
- What is the perimeter of a square with sides of 10 metres?
- What is the perimeter of a rectangle that is 12 metres wide and 8 metres tall?
Answers:
- 4 + 4 + 4 + 4 = 16 metres
- 6 + 3 + 6 + 3 = 18 metres
- 5 + 7 + 8 = 20 metres
- 10 + 10 + 10 + 10 = 40 metres
- 12 + 8 + 12 + 8 = 40 metres
FAQ
What is perimeter?
Perimeter is the total distance around the edge of a shape. It's like walking all the way around the outside of a shape.
How do I find the perimeter of any shape?
Add up all the sides of the shape. No matter what shape it is, you just count how far you go around the outside.
Can I measure perimeter with steps?
Yes! You can walk around a shape and count your steps to find the perimeter. Just make sure all your steps are the same size.
Why do we need to know perimeter?
Knowing perimeter helps us plan things like how much fencing we need, how far we run around a playground, or how much material we need to build a wall.
What if I don't have a ruler?
You can use any object that's the same size, like paper clips or blocks, to measure the sides of a shape and then add them up.