# Length and Width of a Rectangle given Perimeter Calculator

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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