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KS2 maths – how to measure perimeter

Get your ruler and string at the ready and try these real-world measuring activities for LKS2

Lydia Davison
by Lydia Davison
DOWNLOAD A FREE RESOURCE! KS2 Maths Lesson Plan – Use Real-Life Examples to Learn Perimeter

When we consider perimeter, it is not uncommon to envisage a collection of 2D, not-to-scale rectangles pre-drawn on a worksheet for children to calculate the total length of sides.

Fast forward to assessment or retrieval practice and pupils, pencil in hand, have a 50/50 chance of success – dictated by a toss-up on whether to multiply the sides or add (the infamous area vs perimeter confusion).

At its core, however, perimeter may be one of the most concrete concepts we teach at primary level mathematics.

Research shows that human beings have a greater chance of remembering something if it is part of a meaningful experience, so before children in my class simply equated perimeter with rectangles, we stepped into the garden to make a memory. 

What is perimeter?

Begin by introducing the concept of perimeter with a real-life example.

I took my children outside, sat everybody down and walked around the edge of a marked area (being mindful to clearly model ending in the same position as I began).

I asked for a volunteer to copy what they had observed. Then another. I asked: what did you do to copy me exactly?

Here the children dictated the rules on what success looked like based upon what has been modelled.

Attention, engagement and a critical eye equalled success.  

Taskmaster activities KS2

Then, ask the children to go into the garden or playground and find two leaves.

In real Taskmaster style, I gave children five minutes to find and retrieve the two leaves that they agreed were the most visibly different.

The children worked in their learning pairs for this activity, to promote talk and collaboration.

Circulate the group and listen for those pupils who are already conjecturing about shape, width, length, sides or edges!  

Predict perimeters

Once the leaves are collected, the real excitement can then begin. Inform children that you want to measure the outside of the leaves using string.

Ask pupils to predict which of their leaves they think will use the most string and why. Is it because of the number of sides? Is it due to the length or width?

For my Year 3 children, this was a great opportunity to practise the skill of sifting the wheat from the chaff.

Which qualities of the leaf were relevant and which needed to be left on the playground? 

Start measuring

Now it is time to measure! Begin by modelling to the children how to use the string to measure the perimeter of a leaf.

Go back to the success criteria identified at the beginning of the lesson (e.g. measuring around the outside edge, starting and finishing at the same point and not over or under measuring).

Again, use learning partners to support your children to be successful in their accuracy.

Mark the lengths on the string and encourage pupils to use a ruler or metre stick to measure the string – this is a great chance to practise using a ruler! 


Finally, take the time to reflect and discuss what has been discovered in the session.

Are children surprised by the perimeter of a seemingly ‘small’ leaf?

As children progress through perimeter, and take on area too, the appearance of a shape often throws up misconceptions.

Take this time to apply their initial thinking and give children different regular and irregular polygons and ask them to predict which would have the larger perimeter.

Lydia Davison is a KS2 teacher, with responsibility for Maths and Cognitive Science at a 3-11 primary school in Leicestershire. Follow her on Twitter @davisonmiss

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