X Tables
Maths Adventures

Dinosaur maths quest: perimeter

A story-led junior maths adventure using fossils, footprints and giant timelines 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.

Learning outcome

By the end of this page, you will be able to measure the perimeter of any shape by counting or adding up all the sides. Success signs:
  • You can draw a shape and label all its sides
  • You can add up all the sides to find the perimeter
  • You can measure real objects around your home to find their perimeter
  • You can explain how to find perimeter to a friend or grown-up

Why this matters

Perimeter is important because it helps us know how much fencing we need for a garden, how far a dinosaur walked around a fenced area, or how much ribbon we need to go around a gift box. In the world of dinosaurs, it helps us know how big a safe zone is for a baby dinosaur or how far a dinosaur could travel around a fenced-up area.

How it works

Finding the perimeter means adding up all the sides of a shape. Here's how to do it step by step:
  1. Look at the shape and count how many sides it has
  2. Measure or count the length of each side
  3. Add all the sides together
  4. Write your answer with the right unit (like metres or centimetres)

Examples you can see

Let's imagine you are a dinosaur explorer! You have found a fossil that is shaped like a rectangle. You want to build a fence around it so no one can disturb it. Example 1: Rectangle
  • Length (long side) = 5 metres
  • Width (short side) = 3 metres
  • Perimeter = 5 + 3 + 5 + 3 = 16 metres
Example 2: Square
  • All sides are the same length = 4 metres
  • Perimeter = 4 + 4 + 4 + 4 = 16 metres
Example 3: Triangle
  • Side 1 = 6 metres
  • Side 2 = 6 metres
  • Side 3 = 6 metres
  • Perimeter = 6 + 6 + 6 = 18 metres

Try it as a mini adventure

Dinosaur Fossil Fence Quest You are a dinosaur explorer on a mission to protect a newly discovered fossil. You must build a fence around it to keep it safe. The fossil is shaped like a rectangle that is 7 metres long and 4 metres wide. Your mission:
  1. Draw a rectangle that is 7 metres long and 4 metres wide
  2. Measure each side of your rectangle
  3. Count how many metres of fencing you need
  4. Write your answer: Perimeter = ? metres
Step 1: Draw a rectangle that is 7 metres long and 4 metres wide. Step 2: Label the sides:
  • Long side = 7 metres
  • Long side = 7 metres
  • Short side = 4 metres
  • Short side = 4 metres
Step 3: Add all the sides together:
  • 7 + 7 + 4 + 4 = 22 metres
Step 4: You need 22 metres of fencing to protect the fossil!

Common mistakes

  • Mistake: Only adding two sides instead of all four sides of a rectangle
    Why it happens: Not reading the shape carefully or forgetting to count all sides
    Fix: Always look at all sides of the shape and count each one
  • Mistake: Forgetting to write the unit (metre or centimetre)
    Why it happens: Thinking the number is enough without units
    Fix: Always write the unit at the end of your answer
  • Mistake: Adding sides that are not on the outside of the shape
    Why it happens: Confusing inside and outside of the shape
    Fix: Focus only on the outside edges of the shape

Parent and carer guide

You can help your child by:
  • Playing the perimeter game with them using a ruler or measuring tape
  • Measuring the perimeter of real objects around the house, like a book, a table, or a window
  • Using everyday situations to talk about perimeter: "How far would we walk around the garden?"
  • Encouraging them to draw shapes and label the sides
  • Checking that they include the correct unit in their answers
What to say:
  • "Can you find the perimeter of your toy box?"
  • "How much ribbon would you need to go around this picture frame?"
  • "Let's measure the edge of your bed together"
What not to worry about:
  • They might count a side twice – this is normal for young learners
  • They might forget to write the unit – just remind them gently
  • They might get confused with shapes – help them look at each side carefully

Practice questions

  1. What is the perimeter of a square with sides of 5 metres?
  2. What is the perimeter of a rectangle that is 6 metres long and 3 metres wide?
  3. What is the perimeter of a triangle with sides of 4 metres, 5 metres, and 6 metres?
  4. What is the perimeter of a rectangle that is 8 metres long and 2 metres wide?
  5. What is the perimeter of a square with sides of 3 metres?
Answers:
  1. 5 + 5 + 5 + 5 = 20 metres
  2. 6 + 3 + 6 + 3 = 18 metres
  3. 4 + 5 + 6 = 15 metres
  4. 8 + 2 + 8 + 2 = 20 metres
  5. 3 + 3 + 3 + 3 = 12 metres

FAQ

What is perimeter?

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

How do I find the perimeter of a square?

A square has four equal sides. You can add all four sides together or multiply one side by four. For example, a square with sides of 5 metres has a perimeter of 5 + 5 + 5 + 5 = 20 metres or 5 × 4 = 20 metres.

How is perimeter different from area?

Perimeter is the distance around the outside of a shape, while area is the space inside the shape. For example, a rectangle with sides of 4 and 6 has a perimeter of 20 metres but an area of 24 square metres.

Can I measure perimeter with a ruler?

Yes! You can use a ruler to measure each side of a shape, then add them up to find the perimeter. This works best for smaller shapes.

Why do we need to know perimeter?

Knowing perimeter helps us in many real-life situations like putting up fences, decorating rooms, or planning gardens. It helps us know how much material we need.