Introduction
The area of a rectangle is the amount of space inside it. To find the area, you simply multiply the length by the width. The formula is Area = Length × Width. For example, if a rectangle is 5 meters long and 3 meters wide, its area is 15 square meters. This calculator does the math for you — just enter the length and width, and it will give you the area right away. It works with any unit of measurement, whether you're using inches, feet, centimeters, or meters. This is one of the most basic and useful formulas in geometry, and you'll use it often in school, building projects, and everyday life.
How to Use Our Area of a Rectangle Calculator
Enter the length and width of your rectangle, and this calculator will give you the area right away.
Length: Type in the length of your rectangle. This is how long one side is. You can use any unit, like inches, feet, or meters.
Width: Type in the width of your rectangle. This is how long the other side is. Make sure you use the same unit as the length.
Once you enter both numbers, the calculator multiplies the length times the width to find the area of the rectangle. The answer is given in square units. For example, if you enter the length and width in feet, your area will be in square feet. If you need to convert between square feet and other area measurements, our Square Footage Calculator can help.
Area of a Rectangle
A rectangle is a four-sided shape where every corner forms a 90-degree angle. The two longer sides are usually called the length, and the two shorter sides are called the width. All rectangles have opposite sides that are equal in length and parallel to each other.
The area of a rectangle is the amount of space inside its borders. You find it by multiplying the length by the width. The formula is simple:
Area = length × width
For example, if a rectangle has a length of 8 meters and a width of 5 meters, its area is 8 × 5 = 40 square meters. The answer is always in square units because you are measuring a flat, two-dimensional space.
Other Rectangle Properties You Can Calculate
Besides area, there are two other important measurements for any rectangle:
- Perimeter – The total distance around the outside of the rectangle. The formula is P = 2(length + width). For our example, that would be 2(8 + 5) = 26 meters.
- Diagonal – The straight line that cuts from one corner to the opposite corner. You find it using the Pythagorean theorem: d = √(length² + width²). In our example, d = √(64 + 25) = √89 ≈ 9.434 meters. If you need to work with right triangles formed by the diagonal, our Right Triangle Calculator is a great companion tool.
Working Backwards from What You Know
You do not always start with the length and width. Sometimes you might know the area and one side, or the perimeter and the diagonal. As long as you have any two of the five rectangle properties — length, width, area, perimeter, or diagonal — you can solve for the other three. The calculator above supports all ten possible combinations of two known values, so you can work with whatever measurements you have. Some of these combinations involve solving a quadratic equation, which the calculator handles automatically.
Where This Is Useful
Calculating rectangle area comes up all the time in everyday life. You need it when figuring out how much paint covers a wall, how much carpet fills a room, how many tiles fit on a floor, or how large a garden bed is. Builders, architects, and engineers use these formulas daily, but they are just as handy for school projects and home improvement tasks. For related shapes, you might also find our Triangle Area Calculator or Circle Area Calculator useful.
Key Things to Remember
- Always make sure both measurements use the same unit before multiplying. If the length is in feet and the width is in inches, convert one so they match.
- Area is measured in square units (m², ft², cm², etc.), while perimeter and diagonal are measured in regular linear units (m, ft, cm, etc.).
- A square is a special type of rectangle where the length and width are the same. All rectangle formulas still work for squares.
- If you are working with three-dimensional rectangular shapes, you may want to look at volume calculators such as our Cylinder Volume Calculator or Sphere Volume Calculator for other common solids.
- For finding the distance between two points or the midpoint of a line segment, we have dedicated tools that pair well with rectangle geometry problems.