How to Find the Area of a Rectangle: Easy Steps

Whether you’re measuring the square footage of a room or just need to pass your next math test, finding the area of a rectangle is a simple and valuable skill to learn: all you have to do is multiply the rectangle’s length times its width! In this article, we’ll walk you through how to calculate rectangular area with tips from math tutors and teachers (including how to find it when you know the diagonal of the rectangle). We’ve also got a downloadable PDF of practice problems to help you feel confident before your next quiz!

Rectangle Area Formula

Math tutor David Jia explains that the formula for finding the area of a rectangle is simply length times width, or $A = L * W$ . For example, say you have a rectangle with a length of 5 feet and a width of 2 feet. Since 5 times 2 is 10, the rectangle’s area is 10 square feet (10 ft²).

Section 1 of 4:

Finding the Area of a Rectangle

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1
Identify the length and width of the rectangle. For most math problems, the length and width will be indicated on a diagram or in the wording of the question. If you’re finding the area of a real-life rectangle (like a living room floor or tabletop), you’ll need to measure the sides and write down your measurements. ^{[1]
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- In this example, the length $L$ is 5cm and the width $W$ is 4cm.
- Note that in geometry, matching hatch marks on opposite sides of a rectangle mean that the lengths of the two sides are the same.
Meet the wikiHow Experts

David Jia is a math expert and academic tutor with over 10 years of experience with students of all ages and grades in various subjects.

Joseph Meyer is a high school math teacher of 7 years and the founder of Sandbox Math, an online learning community dedicated to helping students succeed in Algebra.

Mario Banuelos, PhD is an associate professor of mathematics at California State University, Fresno, with over 8 years of teaching experience.
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Multiply the length times the width. The formula for the area of a rectangle is simple: “If we’re talking about squares or rectangles, it’s just length times width,” Jia explains.^{[2]
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David Jia
Math Tutor

Expert Interview} So, plug your length and width values into the formula $A = L * W$ $A = L * W$ . In this example, we’re using a length of 5cm and a width of 4cm:
- $A = 4 * 5$
- $A = 20$
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State your answer in square units. Your final answer is 20 cm², which means the area of the rectangle is “twenty centimeters squared.”^{[3]
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- Why do you need square units? Area measures the amount of space a shape takes up on a 2-dimensional (2D) plane. A square unit has 2 dimensions—length and width—so when we say the rectangle has an area of 20 centimeters squared, we mean that the shape takes up 20 squares that are 1 centimeter by 1 centimeter.^{[4]
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Section 2 of 4:

Finding Area with One Side & Diagonal Length

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1
Review the Pythagorean Theorem. The Pythagorean Theorem is a formula for finding the third side of a right triangle if you know the values of the other two 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.^{[5]
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- Since a rectangle is comprised of 4 right (90°) angles, the diagonal that cuts through the shape will create a right triangle, so you can apply the Pythagorean Theorem.
- The Pythagorean Theorem is $a^2 + b^2 = c^2$ , where $a$ and $b$ are the sides of the triangle, and $c$ is the hypotenuse, or longest side.^{[6]
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EXPERT TIP

Joseph Meyer
Math Teacher
Joseph Meyer is a High School Math Teacher based in Pittsburgh, Pennsylvania. He is an educator at City Charter High School, where he has been teaching for over 7 years. Joseph is also the founder of Sandbox Math, an online learning community dedicated to helping students succeed in Algebra. His site is set apart by its focus on fostering genuine comprehension through step-by-step understanding (instead of just getting the correct final answer), enabling learners to identify and overcome misunderstandings and confidently take on any test they face. He received his MA in Physics from Case Western Reserve University and his BA in Physics from Baldwin Wallace University.

Joseph Meyer
Math Teacher

Use this visual trick to understand the Pythagorean Theorem. Imagine a right triangle with squares constructed on each leg and the hypotenuse. By rearranging the smaller squares within the larger square, the areas of the smaller squares (a² and b²) will add up visually to the area of the larger square (c²).
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Use the Pythagorean theorem to solve for the missing side of the triangle. Let's say that you have a rectangle with one side ( $a$ $a$ ) of 6cm, one side ( $b$ $b$ ) with an unknown length, and a diagonal (hypotenuse, or $c$ $c$ ) of 10cm. All you have to do is substitute your known quantities into the Pythagorean Theorem and solve:^{[7]
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- $6^{2}+b^{2}=10^{2}$
- $36+b^{2}=100$
- $b^2 = 100 - 36$
- $b^2 = 64$
- $b=8$ (The length of the other side of the triangle, which is also the other side of the rectangle, is 8cm.)
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Multiply the length times the width. Now that you've used the Pythagorean Theorem to find both the length and width of the rectangle, all you have to do is multiply them.^{[8]
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- $A = 6 * 8$
- $A = 48$ (The area of the rectangle is 48cm².)

Section 3 of 4:

What is a rectangle?

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Rectangles are quadrilaterals with 4 right angles and opposite sides that are parallel and of equal length. That’s a long definition, so let’s break it down. Here’s every property of a rectangle:
- Rectangles are quadrilaterals: This means they are 2D shapes with 4 sides that are straight and closed (the lines join up to enclose the shape).
- Rectangles have right angles: Every corner (vertex) where 2 sides meet is exactly 90 degrees.
- Rectangles have parallel opposite sides: The top and bottom lines of the rectangle are parallel to each other, and the left and right lines are also parallel to each other. Being parallel means the distance between the lines is constant throughout their length, and they will never meet or intersect if extended.
- Rectangles have opposite sides of equal length: The top and bottom lines will be the same length as each other, and the left and right sides will be the same length as each other. If one side of the rectangle is 10, for example, then the opposite side’s length will also be 10.
- A square is a rectangle where all sides are the same length. Every square is a rectangle, but not all rectangles are squares! This is why you use the same formula to find the area of a square.^{[9]
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Section 4 of 4:

Real-World Examples of Rectangle Area

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Rectangular area is used to design rooms, furniture, and even clothing! Knowing how to find a rectangular area is useful for more than just acing a geometry quiz. Let’s say you want to carpet your living room and need to know how much carpet to buy—all you have to do is measure the length and width of the room, multiply them together, and you’ll have your answer! But that’s not all:
- Associate professor of mathematics Mario Banuelos, PhD, adds that “If your room is not rectangular, then you would break it up into rectangles so that you can just calculate a lot of little ones with length times width. For example, if your room is L-shaped, then break that up into 2 non-overlapping rectangles, then calculate length times width for both rectangles and add them up.”^{[10]
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  Mario Banuelos, PhD
  Associate Professor of Mathematics
  
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- What about clothes? Tailoring and alterations expert Connie Tao says, “A good way to anticipate how much fabric you need for a robe is to imagine the body as a large rectangle, with length being the height of the person and width being the measurement of the arms outstretched. This will help you calculate how many square yards of fabric are needed to make a robe.”^{[11]
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  Connie Tao
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Calculator, Practice Problems, & Answers

Sample Calculating Area of a Rectangle Calculator

Sample Calculating Area of a Rectangle Practice Problems

Sample Calculating Area of a Rectangle Practice Answers

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How do I find the area in meters?

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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.

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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?

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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.

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

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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.

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All squares are rectangles. However, not all rectangles are squares.

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If you're finding area, your answer will always be in squared units.

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