# Length Of A Rectangle Calculator

Table of contents

How to use the length of a rectangle calculator?How do I calculate the length of a rectangle?Related calculatorsFAQsWelcome to the **length of a rectangle calculator**, where we'll explain **the formula(s) for the length of a rectangle** and **how to find the length of a rectangle**.

## How to use the length of a rectangle calculator?

Using the **length of a rectangle calculator** is easy — there's only two steps!

**Enter the dimensions**that you know of the rectangle.**Find your rectangle length**in the bottom box.- The
**length of a rectangle calculator works both ways**— try changing the rectangle's length and see how its other dimensions are affected. - Not enough to just know how to use the
**length of a rectangle calculator**? Read on to learn how to calculate the length of a rectangle.

## How do I calculate the length of a rectangle?

**Depending on what information you have available**, there are many ways to calculate the length of a rectangle.

- If you have the area
`A`

and width`w`

, its length`h`

is determined as`h = A/w`

. - If you have the perimeter
`P`

and width`w`

, its length can be found with`h = P/2−w`

. - If you have the diagonal
`d`

and width`w`

, it's length is`h = √(d²−w²)`

. - If the rectangle's width is not known, you'd need to simultaneously solve the system of equations above to get the length
`h`

.

That's a lot of different formulas for the length of a rectangle! These are all derived from the many formulas that govern a rectangle's dimensions. Those formulas are:

where:

- $w$ is the rectangle's
**width**; - $h$ is the rectangle's
**length**; - $A$ is the rectangle's
**area**; - $P$ is the rectangle's
**perimeter**; and - $d$ is the length of the rectangle's
**diagonal**, as described by the Pythagorean theorem.

Here's a neat visual:

### What is the length of a rectangle?

A rectangle has four sides. Its sides are paired, so really there are **only two unique dimensions**. Conventionally, **the rectangle's length is the longest** of these two measurements, but when the rectangle is shown to be standing on the floor, **the vertical side** is usually called the length.

### What is the length of a rectangle with diagonal 5 m and width 3 m?

** 4 m**. Because the connected sides of a rectangle are

**perpendicular**, we can use the Pythagoras theorem to work this one out.

- Rearrange the Pythagoras theorem to make the rectangle's length
`h`

the subject:`h = √(d²−w²)`

. - Plug in your values:
`h = √(5²−3²) = √(25-9) = √16 = 4`

.