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Cotmanhay Junior School

Safe, Happy Learning

Week 4 - 5 Length and perimeter

National curriculum content


  • Convert between different units of measure
  • Measure and calculate the perimeter of a rectilinear figure (including squares) in centimetres and metres

    Lesson objectives

  1. Measure in kilometres and metres
  2. Equivalent lengths (kilometres and metres)
  3. Perimeter on a grid
  4. Perimeter of a rectangle
  5. Perimeter of rectilinear shapes
  6. Find missing lengths in rectilinear shapes
  7. Calculate the perimeter of rectilinear shapes
  8. Perimeter of regular polygons
  9. Perimeter of polygons



What we want children to know

  • Convert between different units of measure (for example, metre and centimetre; millimetre and centimetre)
  • Use mathematical knowledge to add and subtract lengths of different shapes.
  • Be able to measure and calculate the perimeter of rectangles (including squares) and other rectilinear shapes.

    What skills we want children to develop

    Use knowledge to solve Reasoning and Problem Solving questions such as:


    What’s the mistake?

    Rosie is measuring a sunflower using a 30cm ruler. Rosie says: “The sunflower is 150cm tall.” Rosie is incorrect. What mistakes might she have made?


    Dexter and Rosie each raise £1 for every 500 metres they walk. They walk 15km. How much money do they each make?


    Which of these?

    Which of these shapes has the longest perimeter? Explore other letters that can be drawn as rectilinear shapes.


    Mathematical Talk

  • If there are 100 cm in 1 metre, how many cm in 3 metres?
  • What might we measure in mm rather than cm?
  • Why does converting measurements to the same unit of length make it easier to add them?
  • How would you work out the difference between the lengths of two objects?
  • Do you need to measure all the sides of a rectangle to find the perimeter?
  • What do you think rectilinear means? What part of the word sound familiar?