Perimeter of Triangle
2026-02-28 11:50 Diff
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Last updated on August 5, 2025

The perimeter of a shape is the total length of its boundary. The sum of all three sides is called the perimeter of a triangle. Perimeter is also used for fencing a property, sewing, and more. In this topic, we will learn about the perimeter of a triangle.

What is the Perimeter of a Triangle?

The perimeter of a triangle is the total length of its three sides. By adding the length of all three sides, we get the perimeter of the shape.

The formula for perimeter of a triangle is 𝑷 = 𝑎  + 𝑏  + 𝑐, where a, b, and c are the sides of the triangle. For instance, if a triangle has sides, a = 6, b = 8, and c = 10, then its perimeter is p = 6 + 8 + 10 = 24. 

Formula for Perimeter of Triangle - 𝑷 = 𝑎 + 𝑏 + 𝑐.

Let’s consider another example of a triangle with side lengths, 𝑎 = 8, 𝑏 = 10, and 𝑐 = 12. So the perimeter of the triangle will be: 𝑷 = 𝑎 + 𝑏 + 𝑐 = 8 + 10 + 12 = 30.

How to Calculate the Perimeter of Triangle

To find the perimeter of a triangle, we just need to apply the given formula and sum all the sides of the triangle.

For instance, a given triangle has the sides of a = 6, b = 6, c = 6. Perimeter = sum of all sides = 6 + 6 + 6 = 18 cm. 

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Example Problem on Perimeter of Triangle

For finding the perimeter of a triangle, we use the formula, 𝑷 = 𝑎  + 𝑏  + 𝑐. 

For example, let’s say, a = 5 cm, b = 4 cm, and c = 2 cm. Now, the perimeter = sum of all sides = 5 + 4 + 2 = 11cm

Therefore, the perimeter of the triangle is 11 cm.

Tips and Tricks for Perimeter of Triangle

Learning some tips and tricks makes it easier for children to calculate the perimeter of triangles. Here are some tips and tricks given below:

  • Always remember that a triangle's perimeter is simply the sum of the three sides of the shape. For that, use the formula, 𝑷 =  𝑎  + 𝑏  + 𝑐.
  • Calculating the perimeter of a triangle starts by determining the length of each side using the distance formula. The distance formula is: Distance = √(x2-x1)2+(y2-y1)2 Here (x1, y1) and (x2, y2), Indicating the positions of two points that make out a triangle’s side. They can be found by adding the lengths of three sides after they are calculated.
  • To reduce the confusion, specifically, arrange the indicated side lengths if you need the perimeter of a group of triangles. After that, apply the formula to each triangle.
  • To avoid mistakes when adding the perimeter, make sure the side lengths are precise and constant for common uses like gardening and architecture.  
  • If you are given the semi-perimeter, which is half the perimeter, you can multiply it by 2 to determine the full perimeter. Area-related calculations, like Heron’s formula, often use the semi-perimeter. 

Common Mistakes and How to Avoid Them in Perimeter of Triangle

Did you know that while working with the perimeter of a triangle, children might encounter some errors or difficulties? We have many solutions to resolve these problems. Here are some given below:

Problem 1

A triangular-shaped road sign has a perimeter of 48 inches and two sides, the two sides measuring 17 inches each. To find out the missing side of the road, subtract the sum of the known sides from the total perimeter.

Okay, lets begin

Length of the missing side = 14 inches.

Explanation

Let ‘b’ be the side of the missing side.

And the given perimeter = 48 inches.

Length of the two equal sides = 17 inches.

Perimeter of triangle = sum of lengths of three sides.

 48 = 17 + 17 + b

 48 = 34 + b

 b = 48 – 34 = 14

 b = 14

Therefore, the missing side is 14 inches.

Well explained 👍

Problem 2

A wire with a perimeter of 297 inches is reshaped into an equilateral triangle. Find the length of each side of the triangle and divide the total length by 3.

Okay, lets begin

99 inches

Explanation

Given that the perimeter of a rectangle is equal to the total length of the wire and this wire is reshaped into an equilateral triangle, here is the solution:

Perimeter of a rectangle = Total length of the wire

Length of the wire used = Perimeter of the triangle formed

Perimeter of an equilateral triangle = 3 × a

297= 3 × a

297 ÷ 3 = 99

a = 99

Therefore, the length of each side of the triangle is 99 inches.

Well explained 👍

Problem 3

Find the perimeter of an equilateral triangle whose sides are 10cm.

Okay, lets begin

30 cm

Explanation

Perimeter of triangle = a + b + c

P = 10 + 10 + 10 = 30

Therefore, the perimeter of the triangle is 30 cm.

Well explained 👍

Problem 4

Annie is planning a triangular vegetable garden in her backyard. She measures the three sides of the garden: Side A = 12 meters Side B = 9 meters Side C = 15 meters How much string should Annie buy to go around the edge of the garden?

Okay, lets begin

Annie will need 36 meters of string to go around the garden.

Explanation

The perimeter of a triangle is the sum of all the three sides. Using the formula:

P = a + b + c

P = 12 + 9 + 15 = 36 meters.

Well explained 👍

Problem 5

Find the perimeter of the scalene triangular rock.

Okay, lets begin

Sides are a = 10, b = 8, c = 7

Perimeter = a + b + c

= 10 + 8 + 7 = 25 meters.

Explanation

Each side of the scalene triangle has a different length. The entire distance is calculated around the rock to be 25 meters by summing the lengths of the three sides.

Well explained 👍

FAQs on Perimeter of Triangle

1.Evaluate the triangle’s perimeter if its sides are 3cm, 4cm, and 6cm.

Perimeter of triangle = a + b + c, Hence p = 3 + 4 + 6 = 13 cm.

2.What is meant by a triangle’s perimeter?

The total length around a triangle’s sides is its perimeter. In other words, the perimeter of a triangle is the total length of its sides.

3.What are the types of triangles?

There are six types of triangles: Equilateral triangle, Isosceles triangle, Scalene triangle, Acute triangle, right triangle, and obtuse triangle.

4.Which triangle has no equal sides?

A scalene triangle is a triangle with no equal sides. All three sides of the scalene triangle are different.

5. Which triangle has the smallest perimeter?

The orthic triangle has the smallest perimeter. 

Important Glossaries for Perimeter of Triangle

  • Perimeter: The total length of the sides of a shape.
  • Triangle: A polygon with three sides and three angles.
  • Formula of perimeter: The mathematical expression used to calculate the perimeter of a triangle is 𝑷 = 𝑎  + 𝑏  + 𝑐.

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