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 line 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.
Any shape that lie on flat surface and have 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 centimeter (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.
FORMULA FOR PERIMETER
We know every shape is different from one another. Thus, 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.
Rectangle: Rectangle is a four-sided polygon having two dimensions i.e. length and breadth.
Perimeter of a rectangle = sum of four sides
= 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)
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
Square: Square is also a polygon where all its sides are same.
Perimeter of a square = sum of all four sides
= a + a + a+ a
= 4a
Perimeter of a square = 4 side
To learn more about different topics download Byju’s – The Learning App from Google Play Store and watch interactive videos. Also, take free tests to practice for exams.