Area Of Rectangle Calculator

What this calculator does

This is the most everyday area there is. A rectangle has a length and a width, and the space inside it is simply the two multiplied together. A floor, a sheet of paper, a wall, a plot of land.

Type the length and the width, pick your units, and the tool gives you the area.

Using the calculator

1. Type the length and pick its unit.
2. Type the width and pick its unit.
3. Press Calculate.

Both values need to be positive. The two can be in different units, since the tool lines them up before multiplying.

The formula | area = length × width

The area of a rectangle is:

area = length × width

That is the whole formula. There is no constant, no halving, no square root. Just the two sides multiplied.

The formula every other area is built on

This one looks too simple to need its own page, but it is worth understanding properly, because it is the root that every other area formula grows from.

Picture the rectangle covered in a grid of unit squares: the length tells you how many squares sit across, the width how many rows there are, so length × width is the total count of squares, and each square is one unit of area. That counting is what "area" actually means. From there, a triangle's ½ × base × height is just half of a rectangle, and a circle's π × radius² is what you get when the grid is allowed to wrap into a curve. Get the rectangle, and you have the idea behind all of them.

Units, mixed units, and rounding

The area comes out in square units of the length's unit, since you are multiplying a length by a length. The length and width can be in different units: the tool converts the width into the length's unit first, then gives the area in that unit squared. A tidy result is shown in full, and a long decimal is rounded to three places.

A worked example | 8 cm by 5 cm

Say the length is 8 cm and the width is 5 cm.

1. Multiply the two: 8 × 5 = 40.

So the area is 40 cm². Mixed units behave the same way: a length of 2 m and a width of 50 cm becomes 2 m by 0.5 m, giving 2 × 0.5 = 1 m².

Questions people ask

What is the area of a rectangle 8 by 5?

It is 40 square units. Multiply the length by the width: 8 × 5.

Why is the answer in square units?

Because area counts unit squares, and you are multiplying a length by a length. A length and width in centimetres give an area in square centimetres.

Can the length and width be in different units?

Yes. The tool converts the width into the length's unit before multiplying, and labels the area in the length's unit squared.

What is the difference between this and the area of a square?

A square is a rectangle whose length and width happen to be equal, so its area is just side × side. For equal sides the area of square calculator needs only the one number.

How does this relate to a triangle's area?

A triangle with the same base and height is exactly half of a rectangle, which is why its area is ½ × base × height. The area of triangle calculator handles that case.

References

A note on where this comes from. That the area of a rectangle is its length times its width is the foundation on which plane area is measured, the idea of counting unit squares, treated formally by Euclid in the Elements, where the areas of rectangles underpin the rest of plane geometry. For further reading, see Rectangle.

1. Euclid, Elements, Book II (c. 300 BCE), the geometric treatment of rectangles and the areas they enclose.