📐 Perimeter 📚 Grade 3-4 ⏱ 6 min
Perimeter of Any Polygon: Not Just Rectangles
After the rectangle and square formulas, it matters to understand: the perimeter of any shape is simply the sum of all its sides.
The universal perimeter rule
Perimeter is the sum of all a shape's side lengths, regardless of its type. The rectangle has a shortcut formula, but the rule works for any polygon.
💡 Formula check: show that the rectangle formula P=(a+b)×2 is just a quick way to add a+b+a+b.
Perimeter of an irregular shape
A pentagon with sides 3, 4, 5, 2, 6 cm. The perimeter is simply the sum: 3+4+5+2+6=20 cm. No formula here, just addition.
FAQ
Do kids need to memorize a formula for every shape?
No, understanding the general principle is enough — perimeter is the sum of sides; formulas just speed up counting for symmetric shapes.