Perimeter of a Triangle Definition, Formula & Examples | How to Find the Perimeter of a Triangle?

Polygons are the most important topic among all math concepts. One of the simplest polygons is Triangle and the easiest way to work with polygons is by calculating their perimeter. The term perimeter is a path that encloses an area. It completely refers total length of the edges or sides of a given polygon or a two-dimensional figure with angles. So, make sure you move down the page till to an end and learn the perimeter of a triangle definition, formula, and how to calculate the triangle perimeter easily & quickly.

What is the Perimeter of a Triangle?

The definition of Perimeter of a Triangle is the sum of the lengths of the side of the Triangle. It denotes as,

Perimeter = Sum of the three sides

In real-life problems, a perimeter of a triangle can be useful in building a fence around the triangular parcel, tying up a triangular box with ribbon, or estimating the lace required for binding a triangular pennant, etc.

Always, the result of the triangle perimeter should be represented in units. If the side lengths of the triangle are measured in centimeters, then the final result needs to be in centimeters.

Formula to Calculate Perimeter of Triangle

The basic formula is surprisingly uncomplicated. Simply add up the lengths of all of the triangle sides and you get the perimeter value of the given triangle. In the case of the triangle, if the sides are a,b,c then the perimeter of a triangle formula is P = a + b + c.

How to Find the Perimeter of a Triangle?

Between Area and Perimeter of a Triangle calculation, finding the perimeter of the triangle is the easiest one and it has three ways to calculate the triangle perimeter. All the three ways used to find the triangle perimeter are mentioned here for your sake of knowledge and understanding the concept efficiently. The ways to find the perimeter of a triangle are as follows:

  1. The first & simple way is when side lengths are given, then we have to add them together to get the perimeter of the given triangle.
  2. If we have two sides and then solve for a missing side using the Pythagorean theorem.
  3. In case, we have the side-angle-side information in the given question, then we can solve for the missing side with the help of the Law of Cosines.

For a better explanation of the concept, we have listed out some worked-out examples of calculating the perimeter of a triangle below. Have a look at the solved examples and understand the concept behind solving the perimeter of a polygon ie., a Triangle.

Solved Examples on Finding Perimeter of a Triangle

1. Find the perimeter of the triangle where the three sides of the triangle are 20 cm, 34 cm, 15 cm?


Given Sides of the triangle are a = 20 cm, b = 34 c, c = 15 cm

Now, use the Perimeter of Triangle Formula and find the result,

Perimeter = (a + b + c) 

= 20 + 34 + 15 = 69 cm.

2. Find the missing side whose perimeter is 40 cm and two sides of the triangles are 15 cm?



a = 15 cm
b = 15 cm
P = 40 cm

Find c, Let’s assume c=x

Perimeter of the triangle P = a + b + c

40 cm = 15 cm + 15 cm + x

40 cm = 30 cm + x

x = 40 cm – 30 cm

x = 10 cm

Therefore, the length of the third side of the triangle is 10 cm.

FAQs on Calculating Triangle Perimeter

1. What are the types of Triangles and their perimeter formulas?

There are 4 types of triangles. They are listed below with their perimeter formulas:

  1. Equilateral triangle: Perimeter (P) = 3 x l
  2. Right triangle: Perimeter (P) = a + b + c
  3. Isosceles triangle: Perimeter (P) = 2 x l + b
  4. Scalene triangle: Perimeter (P) = b + p + h where h2 = b2 + p2

2. What is the formula of the perimeter of a triangle?

If a triangle has three sides a, b and c, then, the formula for the perimeter of a triangle is Perimeter, P = a + b +c.

3. How do you calculate the perimeter of a triangle with known sides?

If we knew the sides of a triangle, then finding the perimeter is so simple, just apply the perimeter of a triangle formula ie., P = a + b +c. and substitute all the sides and add them together.

Leave a Comment