Perimeter
The perimeter is the distance all the way around a shape — the length you'd walk if you started at a corner and went all the way back to the start.
Perimeter = sum of all sides.
Triangle
A triangle has 3 sides. Sum them:
sides 5, 7, 6 → P = 5 + 7 + 6 = 18.
Rectangle
A rectangle has 4 sides — but 2 pairs are equal.
sides 6 and 4 → P = 6 + 4 + 6 + 4 = 20.
A nice trick: P = 2 × (a + b).
2 × (6 + 4) = 2 × 10 = 20. ✓
Square
A square has 4 equal sides.
side 5 → P = 5 + 5 + 5 + 5 = 20.
Trick: P = 4 × side.
4 × 5 = 20. ✓
Bigger polygons
For any polygon, the rule is the same — add up all the sides.
Pentagon with sides 3, 4, 5, 6, 7: P = 3 + 4 + 5 + 6 + 7 = 25.
Real-life perimeter
- Length of a fence around a garden.
- How long a picture frame must be.
- Walking distance around a square.
Watch the units
Always include the unit. Perimeter = 20 cm, not just "20".
Try it
Summary
- Perimeter = sum of all sides.
- Square: 4 × side. Rectangle: 2 × (a + b).
- Always include the unit.