How to Find the Length and Width of a Rectangle When Given the Area

By Kat Walcott; Updated April 24, 2017
If you know the area and length or area and width of a rectangle, you can easily determine the other unknown value.

Though you cannot determine both the width and length of a rectangle at the same time with just the area, if you know the area and either the length or width, you can find out the measurement of the other side. If you are already familiar with the formula for area -- length times width -- this can be done in just a few steps.

Finding the Length

The area of a rectangle is the length multiplied by the width or L x W. Therefore, to determine an unknown length, you simply need to divide the area by the width. For example, if the area of a rectangle is 50 and the width is 20, the equation would be 50 divided by 20 equals 2.5 -- making a very long, narrow rectangle. You can double-check your answer by plugging this value into the formula for area -- L x W -- to see if you get the area you were given. In the example, 2.5 multiplied by 20 is indeed 50, so the answer is correct.

Finding the Width

Find the unknown width of a rectangle by dividing the area by the length. If the area is 25 and the length is 4, the equation would be 25 divided by 4 equals 6.25. Double-check your answer by plugging this value into the formula for area -- L x W -- to see if you get the area you were originally given. 4 multiplied by 6.25 equals 25, so the answer is correct.

About the Author

Based in Gatineau, Canada, Kat Walcott has been writing entertainment and informative articles since 2008. Her work has appeared in major publications including Her Campus, Equals6 and Uppercase. She holds an honors diploma in social science from Heritage College and is currently majoring in communication studies and minoring in sexuality studies.