Rectangle Area Calculator
Find the area and perimeter of a rectangle.
Results update as you type.
How it works
A rectangle is a four-sided shape with four right angles, where opposite sides are equal in length. It is one of the most common shapes in everyday life, from rooms and screens to sheets of paper and plots of land, which makes calculating its area and perimeter a frequent, practical task. This rectangle area calculator takes the length and the width and returns both the area, the amount of surface the rectangle covers, and the perimeter, the distance around its edge. The area is found by multiplying the length by the width, and it is measured in square units such as square metres or square feet. The perimeter is found by adding up all four sides, which because opposite sides match is simply twice the sum of the length and the width, measured in ordinary linear units. For a rectangle 5 units long and 3 units wide, the area is 15 square units and the perimeter is 16 units. Homeowners estimating flooring or paint, gardeners planning beds, designers sizing layouts, and students learning geometry all use a rectangle area calculator to get both measurements at once without the risk of mixing up the two formulas.
area = length × width; perimeter = 2 × (length + width)
The area of a rectangle is the length multiplied by the width because a rectangle can be tiled by rows and columns of unit squares, and the count of those squares is exactly the product of the two side lengths. The perimeter is the total distance around the outside, so you add the two lengths and the two widths, which simplifies to twice the sum of one length and one width because opposite sides are equal.
Source:Euclidean geometry
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter length and width.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Area updates instantly as you type — no button to press.
Frequently asked questions
How do I find the area of a rectangle?
Multiply the length by the width. Both measurements must be in the same unit, and the result is in square units of that measure, such as square metres or square feet. For a rectangle that is 5 metres long and 3 metres wide, the area is 5 times 3, which equals 15 square metres. The calculator does this multiplication for you and also returns the perimeter alongside it.
What is the difference between area and perimeter?
Area measures the flat space a rectangle covers and is given in square units, while perimeter measures the total length of its boundary and is given in ordinary linear units. Area answers how much surface there is to paint or carpet, whereas perimeter answers how much fencing or trim you need around the edge. They are calculated differently and describe two genuinely different properties of the same shape.
Do length and width need the same units?
Yes. Both sides must be expressed in the same unit before you multiply or add them, or the result will be meaningless. If one side is in metres and the other in centimetres, convert one first so they match. Once the units agree, the area comes out in that unit squared and the perimeter in that unit, and the calculator assumes consistent units throughout.
How is the area of a square related?
A square is a special rectangle whose length and width are equal, so its area is simply one side multiplied by itself, or the side squared. You can use this rectangle calculator for a square by entering the same value for both the length and the width. The perimeter of a square then works out to four times the side length, since all four sides are identical.
Can I use decimals for length and width?
Absolutely. Real measurements rarely land on whole numbers, so the calculator accepts decimal values for both the length and the width. Entering 5.5 by 3.25, for example, returns a precise area and perimeter without rounding your inputs. This is useful for room dimensions, fabric, and any measurement taken with a tape or ruler where fractional units are the norm rather than the exception.