Perimeter is the total distance all the way around a shape.

Simple definition

  • For any 2D shape (like a rectangle, triangle, or polygon), the perimeter is the sum of the lengths of all its sides.
  • For a circle, the perimeter has a special name: circumference , and it measures the distance around the circle.

Think of walking around a field along the fence: the distance you walk is the perimeter of that field.

Basic formulas

  • Any polygon: add all side lengths, P=side1+side2+…P=\text{side}_1+\text{side}_2+\dots P=side1​+side2​+….
  • Rectangle: P=2(length+width)P=2(\text{length}+\text{width})P=2(length+width).
  • Square: P=4×sideP=4\times \text{side}P=4×side.
  • Triangle: P=a+b+cP=a+b+cP=a+b+c (add the three sides).
  • Circle (circumference): P=2πrP=2\pi rP=2πr, where rrr is the radius.

Quick example

  • A rectangle is 5 cm long and 3 cm wide.
    • Perimeter: P=2(5+3)=2×8=16P=2(5+3)=2\times 8=16P=2(5+3)=2×8=16 cm.

So, whenever you see “what is the perimeter,” it’s asking, “How far is it if you go all the way around this shape?”