Perimeter
- CBSE · NCERT Class 6, Ch 6 Perimeter and Area
The perimeter of a flat shape is the total length of its boundary, the distance you would walk going once all the way round it.
Perimeter measures the edge of a shape, not the space inside it. For a shape made of straight sides, you add up the lengths of all the sides. It is a length, so it is measured in cm, m or km.
Two rules save time:
- Rectangle: perimeter = 2 × (length + breadth).
- Square: perimeter = 4 × side.
The boundary of a circle has its own name, the circumference. It equals 2πr, where r is the radius.
A small example
A garden is 18 m long and 12 m wide. A fence goes all round it. How much fencing is needed? Perimeter = 2 × (18 + 12) = 2 × 30 = 60 m.
Now suppose a 3 m gate is left without fence. The fencing needed is 60 - 3 = 57 m. Reading which parts of the boundary count is half the question.
Why it matters later
In Class 10 Chapter 11 the boundary is partly curved. The perimeter of a sector is two radii plus the length of the arc. Leaving out the two straight edges is an easy way to lose marks. The idea is the same one from Class 6: walk the whole boundary once and add up every piece.
Sources
Facts last checked against these sources on 30 September 2026.
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