How to Calculate the Area of a Rectangle

Co-authored by David Jia

Last Updated: March 10, 2023 References

A rectangle is a quadrilateral^{[1]
X
Research source} with two sides of equal length and two sides of equal width that contains four right angles. To find the area of a rectangle, all you have to do is multiply its length with its width. If you want to know how to find the area of a rectangle, just follow these easy steps.

Method 1

Method 1 of 3:

Understand the Basics of a Rectangle

1
Understand the rectangle. The rectangle is a quadrilateral, which means it has four sides.^{[2]
X
Research source} Its opposite sides are equal in length, so the sides along its length are equal, and the sides along its width are equal as well. If one side of the rectangle is 10, for example, then the opposite side's length will also be 10.
- Also, every square is a rectangle, but not all rectangles are squares. So treat squares like rectangles in terms of finding its area.
2
Learn the equation for finding the area of a rectangle. The equation for finding the area of a rectangle is simply A = L * W.^{[3]
X
Research source} This means that the area is equal to the length of the rectangle times its width.

Method 2

Method 2 of 3:

Find the Area of a Rectangle

1
Find the length of the rectangle. In most cases, you will be given the length, but if not, you can find it using a ruler.^{[4]
X
Research source}^{[5]
X
Research source}
- Note that the double hash marks on the long sides of the rectangle mean that the lengths of the two sides are the same.
2
Find the width of the rectangle. Use the same methods to find it.^{[6]
X
Research source}
- Note that the single hash marks on the wide sides of the rectangle mean that the two widths have equal length.
3
Write the length and width next to each other. In this example, the length is 5 cm and the width is 4 cm.
4
Multiply the length times the width. Your length is 5 cm and your width is 4 cm, so you should plug them into the equation A = L * W to find the area.^{[7]
X
Research source}
- A = 4 cm * 5 cm
- A = 20 cm^2
5
State your answer in square units. Your final answer is 20 cm^2, which means "twenty centimeters squared."^{[8]
X
Research source}
- You can write your final answer in one of two ways: either 20 cm.sq. or 20 cm^2.

Method 3

Method 3 of 3:

Find the Area if You Only Know the Length of One Side and the Diagonal

1
Understand the Pythagorean theorem. The Pythagorean theorem is a formula for finding the third side of a right triangle if you know the value of two of the sides. You can use it to find the hypotenuse of a triangle, which is its longest side, or its length or width, which meet at a right angle.^{[9]
X
Research source}
- Since a rectangle is comprised of four right angles, the diagonal that cuts through the shape will create a right triangle, so you can apply the Pythagorean theorem.
- The theorem is: a^2 + b^2 = c^2, where a and b are sides of the triangle and c is the hypotenuse, or longest side.^{[10]
  X
  Research source}
2
Use the Pythagorean theorem to solve for the other side of the triangle. Let's say that you have a rectangle with a side of 6 cm and a diagonal of 10 cm. Use 6 cm for one side, use b for the other side, and take 10 cm as your hypotenuse. Now just substitute your known quantities into the Pythagorean theorem and solve. Here's how to do it:^{[11]
X
Research source}
- Ex: 6^2 + b^2 = 10^2
- 36 + b^2 = 100
- b^2 = 100 - 36
- b^2 = 64
- square root (b) = square root (64)
- b = 8
  - The length of the other side of the triangle, which is also the other side of the rectangle, is 8 cm.
3
Multiply the length times the width. Now that you've used the Pythagorean theorem to find the length and width of the rectangle, all you have to do is multiply them.^{[12]
X
Research source}
- Ex: 6 cm * 8 cm = 48 cm^2
4
State your answer in square units. Your final answer is 48 cm^2, or 48 cm. sq.

Calculator, Practice Problems, and Answers

Sample Calculating Area of a Rectangle Calculator

Sample Calculating Area of a Rectangle Practice Problems

Sample Calculating Area of a Rectangle Practice Answers

Community Q&A

Question

How do I find the area in meters?

Community Answer

You cannot find an area in meters, because area is expressed in square meters. If the values of your rectangle sides are not in meters, then you must first convert those units to meters, and then multiply the converted values to get the area in square meters.
Question

If the problem says length is 105 breadth is 81 and other said of length is 103 and breadth is 53, how do I find the area of the rectangle?

Community Answer

A rectangle has 2 sides of equal length and 2 sides of equal width (breadth). By definition, the object in which you are describing is not a rectangle. The object you have is an irregular quadrilateral.
Question

How do I find the area of a rectangle when each side is a different length?

Community Answer

It is not a rectangle if each side is a different length. It is either an irregular shape or a trapezoid. There is no formula for finding the area of an irregular shape. The area of a trapezoid is found by multiplying its height by the average of its bases.