# Math Study Help: Finding the Perimeter

By Suvo

Find a review of the how to find the perimeter of an area in this math study guide.

Like area, perimeter is another important parameter for defining a plane geometric shape. In this study guide we will discuss the perimeter of a circle, triangle, rectangle and square.

## What is Perimeter?

Perimeter is the total length of the outer boundary of any plane area. The outer boundary of a plane area may be either a smooth curve or connected line segments or a combination of both. Finding the perimeter means calculating the total length of the boundary curve or line segments.

## Formulas

• Circle: The perimeter of a circle can be calculated using the following formula:

P = 2 * Π * R…………Eqn.1

Where,

P – Perimeter of the circle.

R – Radius of the circle.

• Triangle: The perimeter of a triangle can be calculated using the following formula:

P = A + B + C ……….Eqn.2

Where,

P is the perimeter of the triangle.

A, B, C are the three sides of the triangle.

For equilateral triangles, Eqn.2 can be modified as:

P = 3 * A……………..Eqn.3

Where,

A is the length of the sides of the triangle.

For isosceles triangles, Eqn.2 can be modified as:

P = (2 * A) + B ……..Eqn.4

Where,

A is the length of the equal sides of the triangle.

B is the unequal side length.

• Rectangle: The following formula is used for finding the perimeter of rectangle:

P = 2 * (A +B)……….Eqn.5

Where,

P is perimeter of the rectangle.

A and B are the length of the two sides of the rectangle.

• Square: A square is a special rectangle, which has equal sides . So, from Eqn.5, we can write formulae for finding perimeter of square as below:

P = 4 * A ……………Eqn.6

Where,

P is the perimeter of the square.

A is the length of the sides.

## Units

Finding perimeter means calculating the total length of the boundary curve or line segments, so the units are the same as units of length (i.e., mm, inch, meter etc.)

## Practice Problems

1. What is the perimeter of a triangle with a base of 4 mm and two sides of 2 mm and 6 mm?
2. Find the perimeter of an equilateral triangle, whose sides are 10 mm long?
3. Find the area of the rectangle, which has two sides of 10 inches and 5 inches?