# Perimeter of a Rectangle

LAST UPDATE: February 2nd, 2022

## Method #1 – Perimeter from Length & Width

### Formula – How to calculate the perimeter of a rectangle from the length & width

Perimeter = 2 x Length + 2 x Width

##### Example

A rectangle has a length of 10 and a width of 30.

Perimeter = 10 x 2 + 30 x 2 = 20 + 60 = 80

## Method #2 – Perimeter from Area

### Formula – How to calculate the perimeter of a triangle from the Area and one side

Step 1: Calculate the width

Width = Area ÷ Length

Step 2: Calculate the perimeter

Perimeter = 2 x Length + 2 x Width

##### Example

A rectangle has a length of 10 and an area 400.

Width = 400 ÷ 10 = 40

Perimeter = 2 x 10 + 2 x 40 = 20 + 80 = 100

## Method #3 – Perimeter from the Diagonal

### Formula – How to calculate the perimeter of a rectangle from the diagonal

Step 1: Calculate the width

Width = √(Diagonal2 – Length2)

Step 2: Calculate the perimeter

Perimeter = 2 x Length + 2 x Width

##### Example

A rectangle has a length of 10 and a diagonal of 30.

Width = √(302 – 102) = √(900 – 100) = √800 = 28.2843

Perimeter = 2 x 10 + 2 x 28.2843 = 20 + 56.5686 = 76.5686