· Grade 3 lesson · 2 min read
Lesson: Area vs. Perimeter (Grade 3)
Perimeter goes AROUND. Area fills the INSIDE.
One picture, two ideas
This rectangle is 5 cm long and 3 cm wide.
Perimeter: walk around it 🟧
Perimeter is the orange line. Imagine an ant walking all the way around the edge.
Add up every side:
5 + 3 + 5 + 3 = 16 cm
Area: fill it up 🟦
Area is the blue squares inside. Count them: there are 15.
A faster way: there are 3 rows of 5 squares.
5 × 3 = 15 square cm
How to remember
| Perimeter | Area | |
|---|---|---|
| Think of… | a fence | a carpet |
| What to do | add all the sides | count the squares (or length × width) |
| Answer in | cm | square cm (cm²) |
A fun surprise
These two shapes have the same fence (perimeter 16), but different carpet (area)!
Draw them on squared paper and count. It's a great "wow" moment!
Practice
Start with Area & Perimeter. Then try Area of Composite Figures for L-shaped rooms.