Math // Measurement

Measuring Perimeters

Measure the perimeter of simple 2-D shapes

Ages
7 to 8
Type
Method
Builds on
2 topics
Leads to
1 topic
Standards
1 code

Quick check

If the learner wants to put a decorative border around a rectangular picture frame 20 cm wide and 30 cm tall, can they work out the total length of border needed?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Measure each side of a rectangle and add the lengths to find the perimeter
  • Calculate the perimeter of a regular shape given the side length
  • Explain that perimeter is the total distance around a shape

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

2 topics
  • Calculating with measurementsRequired

    Measurement // Ages 7 to 8

    Measuring perimeter requires measuring lengths and adding them

  • 2-D shapes (age 6+)Helpful

    Geometry // Ages 6 to 7

    Perimeter of 2-D shapes requires knowing shape properties (number of sides)

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Measuring Perimeters

Ages 7 to 8 // Method

Leads to

1 topic
  • Perimeters of polygonsRequired

    Measurement // Ages 8 to 9

    Measuring perimeter of simple shapes is prerequisite to perimeter problem solving

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

Perimeter is the total distance once around the boundary of a 2-D shape — found by measuring every side and adding the lengths, or for a regular shape multiplying one side by the number of sides. The core idea to secure is that perimeter is a length (the once-around distance) and is distinct from area (the surface covered inside). Target age 7–8.

Common misconceptions

  • Adds only the two given sides of a rectangle, forgetting the opposite two.
  • Confuses perimeter with area — counts the squares inside instead of the distance around.
  • For a regular shape, measures one side but doesn't account for all the equal sides.
  • Gives the perimeter as a bare number without a length unit.

Useful representations

  • A shape with each side measured and labelled, summed around the boundary
  • A finger/marker tracing the whole boundary back to the start
  • A regular polygon: one side labelled, perimeter = side × number of sides
  • A rectangle with only two adjacent sides given, the opposite two to be filled in

Teaching practices

  • Define perimeter physically as walking all the way around the edge and back to the start.
  • Measure and label every side, then add — for a rectangle, remind pupils the two unmarked sides equal their opposites.
  • For regular shapes, connect equal sides to multiplication (side length × number of sides).
  • Deliberately contrast perimeter (distance around) with area (surface covered) on the same shape so the two are not confused.
  • Keep the length unit in the answer (cm, m).

Activities to try

  1. 1

    Walk the boundary and build the total

    Why it works: Perimeter is the complete once-around distance: you must account for every side (including hidden equal ones), it is a length with a unit, and for a regular shape equal sides let you multiply instead of adding one by one.

    1. Trace a finger or marker all the way around the edge of a shape, starting and finishing at the same corner, so 'perimeter' is felt as walking once around and back to the start.
    2. On a rectangle that shows only two adjacent side lengths, work out the two hidden opposite sides (opposite sides are equal), label them, then add all four sides.
    3. Keep a running total as you cover each side, and only count the perimeter as complete when the whole boundary has been traced back to the start.
    4. On a regular pentagon with one side labelled, find the perimeter as side length × 5 (or by adding five equal sides) and explain why the shortcut works.
    5. Measure every side of a small irregular shape with a ruler and add the lengths.
  2. 2

    Perimeter is not area

    Why it works: Perimeter (distance around the edge, a length) and area (surface covered inside) are different measures on the very same shape and must not be swapped.

    1. On one straight-sided shape drawn along the lines of a square grid, first trace the boundary and add the side lengths to find the perimeter, then shade the interior and count the unit squares to find the area (in square units).
    2. State in your own words which measure is a distance around the edge and which is the surface covered inside.
    3. Given a question, decide whether it is asking for perimeter or area before you start, and say how you know.
  3. 3

    Spot-the-error and mixed practice

    Why it works: Applying perimeter across rectangle (hidden sides), regular-polygon (side×n), and perimeter-vs-area cases, and critiquing a wrong method, consolidates accurate, unit-bearing reasoning.

    1. Solve fill-the-blank items: a rectangle with only two adjacent sides given (supply the opposite two, then total), and a regular polygon with one side labelled (use side × number of sides).
    2. Judge a worked example where another child added only the two given rectangle sides — say what went wrong and give the correct perimeter.
    3. Answer a mixed item where one option is the area of the shape, choosing and justifying the correct perimeter.
    4. Check every answer carries its length unit.

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
The national curriculum in England: Key stages 1 and 2 framework document
Ma/KS2/Y3/M/2

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