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Length and Width of a Rectangle given Perimeter Calculator

Last updated: July 9, 202428 people find this calculator helpful
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Our length and width of a rectangle given perimeter calculator will help you calculate the unknown side of any rectangle. If you are looking to find the width of a rectangle and already know the perimeter, you have come to the right place. We will share:

  • How to find the unknown sides of a rectangle when the only thing you know is the perimeter.
  • How to find the length of a rectangle given the perimeter and the width.
  • The length of a rectangle formula.
  • The relationship between a square and a rectangle.

🔎 Since a square has all the properties of a rectangle, we say a square is a type of rectangle. However, not all rectangles are squares.

How to find the length and width of a rectangle given the perimeter

Generally, if you are given the perimeter of a rectangle and asked to find the length and width, this would be impossible unless the rectangle also happens to be a square. Because all the sides of a square are equal, finding both length and width would be possible.

The formula for the perimeter of a square is: P = 4X, where X is the unknown sides, and P is the perimeter. So to find the width of a square, we would make X the subject of the formula. Our new formula would then read X = P/4.

Find the length of a rectangle given the perimeter

We use a different formula where the rectangle is not also a square. We will need to know the measurement of at least one side. The required inputs are also different. We use one of the following equations for the perimeter of a rectangle.

P = 2(L + W) or P = 2 × L + 2 × W

So using the first equation for the perimeter of a rectangle, let's assume the length of a rectangle is unknown, but you know the perimeter and the width. You then make the unknown value the subject of the formula. The new equation created is our length of rectangle formula. So, from the first formula above, we would get the following equation. It is the formula used by our length and width of a rectangle given perimeter calculator:

  • L = (P/2) - W

To find the width of the rectangle, you would make W the subject of the formula instead.

To use this length and width of a rectangle given the perimeter calculator, we need to input the perimeter and the value of one side.

Let's look at this example: The perimeter of a rectangle is 10 inches, and the width is 3 inches.

Using the formula: L = (P/2) - W

Substitute in the known values:

  • L = 10 / 2 - 3
  • L = 5 - 3 = 2.

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FAQs

What does the Length and Width of a Rectangle given Perimeter Calculator do?
This length and width of a rectangle given perimeter calculator will help you to find the unknown side of a rectangle using the perimeter value. Use the calculator above for instant results in your browser.
Is the Length and Width of a Rectangle given Perimeter Calculator free to use?
Yes. All Try To Calculator tools are free and do not require an account.
Are my inputs stored or sent to a server?
No. Calculations run locally in your browser. We do not collect the numbers you enter or the results shown.
Can I use the Length and Width of a Rectangle given Perimeter Calculator for professional decisions?
This tool is for education and quick estimates. For medical, legal, tax, or financial decisions, verify results with a qualified professional.
Where can I find related calculators?
Browse more Math tools on Try To Calculator at /math, or use the related calculators section on this page.

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