A perimeter is a path that surrounds a two-dimensional shape. The word comes from the Greek - peri (around) and meter (measure). The term may be used either for the path or its length - it can be thought of as the length of the outline of a shape. The perimeter of a circle or ellipse is called its circumference.

Calculating the perimeter has considerable practical applications. The perimeter can be used to calculate the length of fence required to surround a yard or garden. The perimeter of a wheel (its circumference) describes how far it will roll in one revolution. Similarly, the amount of string wound around a spool is related to the spool's perimeter.     

Perimeter is the distance around a two dimensional shape, or the measurement of the distance around something; the length of the boundary. 

Perimeter of a Triangle

The perimeter of a triangle is;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mi»a«/mi»«mo»+«/mo»«mi»b«/mi»«mo»+«/mo»«mi»c«/mi»«/math»

If the triangle is an equilateral triangle;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mn»3«/mn»«mo»§nbsp;«/mo»«mi»x«/mi»«mo»§nbsp;«/mo»«mi»a«/mi»«/math», where, 'a' is the length of the sides.

Perimeter of a Square

The perimeter of a square is;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mn»4«/mn»«mo»§nbsp;«/mo»«mi»x«/mi»«mo»§nbsp;«/mo»«mi»a«/mi»«/math», where, 'a' is the length of the sides.

Perimeter of a Rectangle

The perimeter of a rectangle is;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mn»2«/mn»«mo»(«/mo»«mi»l«/mi»«mo»§nbsp;«/mo»«mi»x«/mi»«mo»§nbsp;«/mo»«mi»b«/mi»«mo»)«/mo»«/math», where, 'l' is the length and 'b' the breath.

Perimeter of a Quadilateral

The perimeter of a quadilateral is;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mi»a«/mi»«mo»+«/mo»«mi»b«/mi»«mo»+«/mo»«mi»c«/mi»«mo»+«/mo»«mi»d«/mi»«/math»

Perimeter of a Circle

The perimeter of a circle is;

«math xmlns=¨¨»«mi»p«/mi»«mo»=«/mo»«mn»2«/mn»«mi»§#960;«/mi»«mi»r«/mi»«/math», where, 'r' is the radius of the circle and '«math xmlns=¨¨»«mi»§#960;«/mi»«/math»' = 3.14.

Example 1: Find the perimeter of a triangle with sides measuring 5 centimeters, 9 centimeters and 11 centimeters. 

Solution:  P = 5 cm + 9 cm + 11 cm = 25 cm  

Example 2: A rectangle has a length of 8 centimeters and a width of 10 centimeters. Find the perimeter.


Solution 1: P = 8 cm + 8 cm + 10 cm + 10 cm = 36 cm.

Solution 2: P = 2(8 cm) + 2(10 cm) = 16 cm + 20 cm = 36 cm. 

The second solution is the more commonly used one.

Example 3: Find the perimeter of a square with each side measuring 2 inches.

Solution 1: P = 2 in + 2 in + 2 in + 2 in = 8 in. 

Solution 2: P = 4x 2in = 8 in.

The second solution is the more commonly used one.

Example 4: Find the perimeter of an equilateral triangle with each side measuring 4 centimeters.

Solution 1: P = 4 cm + 4 cm + 4 cm = 12 cm. 

Solution 2: P = 3 x 4cm = 12 cm

The second solution is the more commonly used one.

A square and an equilateral triangle are both examples of regular polygons. Another method for finding the perimeter of a regular polygon is to multiply the number of sides by the length of one side.  

Example 5: Find the perimeter of a regular pentagon with each side measuring 3 inches.


Solution: = 5 x 3 in = 15 in. 

Example 6: The perimeter of a regular hexagon is 18 centimeters. How long is one side?

Solution: We have P = 18 cm

Let us now find the length of one side.

A regular hexagon has 6 sides, so we can divide the perimeter by 6 to get the length of one side ( S ).

 S = 18 cm / 6

S = 3 cm 


The idea of perimeter is widely used in our daily life.

  • A farmer who wants to fence his field.
  • An engineer who plans to build a compound wall on all sides of a house.
  • A person preparing a track to conduct sports.

All these people use the idea of ‘perimeter’.

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