Third Grade · Math · week 29

Perimeter walks

Find the perimeter of a shape by adding all the side lengths.

Perimeter is the distance ALL the way around a shape — like the fence around a yard. To find it, add up the lengths of every side.

Perimeter is a length, so it uses regular units (inches, feet), not square units. That is the big difference from area: perimeter is the border, area is the inside.

📋 For the teacher
Teach it (10–15 min):
  • Literally walk the perimeter of a room or rug, counting steps.
  • Contrast with area in the same lesson so the two do not blur.
  • Show the 2 × (L + W) shortcut after they add all four sides the long way.
  • Use plain units for perimeter, square units for area.
Talk about it:
  • What is perimeter?
  • What units does perimeter use?
  • How is it different from area?

Mastery looks like: They find perimeter by summing all sides and keep perimeter and area units straight.

Common stumbles: Confusing perimeter with area; missing a side; using square units for perimeter.

See it visually

Interactive, spoken-aloud tools that show this idea in motion.

AdditionSee groups combine — with counters, blocks, and the number line.try →
Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
Records attendance + 15 min of Math for this learner.
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