We come across many shapes in daily life.  Consider a triangle, a rectangle, a square or any other shape. Every shape begins with a line or a line segment or a curve. Number and arrangement of these lines decide the type of figure. Each shape has an interior region or surface bounded by these lines. These bounded lines form the perimeter of a geometric shape and formula for it may vary from one shape to another.
What is the Perimeter?
Any shape that lies on a flat surface and has only two dimensions i.e. length and breadth are called 2-D (two-dimensional) shape. Every polygon is a 2-D figure which lies flat on a plane. Polygons are closed figures which are bounded by a chain of line segments, for example, triangles, rectangles, and squares. Perimeter (peri: around; meter: measure) of a polygon is the distance or linear measure of these bounded line segments. In other words, it is the length of its boundaries. Its unit is centimetre (cm) or meter (m).
Consider a rectangle, the surrounding distance indicated by the arrows form the perimeter of the given rectangle. It is the sum total covered by two lengths and two breadths.
Perimeter of Different Shapes – Formulas
We know every shape is different from one another. Thus, the formula for perimeters of geometric shapes also varies from one shape to another. Some common shapes and formula for finding their perimeters are as follows.
Perimeter of Rectangle
Rectangle is a four-sided polygon having two dimensions i.e. length and breadth.
= ABÂ Â Â Â +Â Â Â Â BCÂ Â Â Â Â Â Â + CDÂ Â Â Â Â Â +Â Â AD
= length + breadth + length + breadth
= 2 length + 2 breadth
Perimeter of a rectangle =  2 × (length + breadth)
Perimeter of Circle
Circle is a collection of points and perimeter of a circle is known as circumference of a circle.
Where r is the radius of the circle and
Perimeter of Square
Square is also a polygon where all its sides are the same.
The perimeter of a square = sum of all four sides
= a + a + a+ a
= 4a
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