Method #1 – Perimeter from Length & Width
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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
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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
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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