Calculators
Rectangle Area & Perimeter
Get a rectangle's area, perimeter and diagonal from its width and height, handy for rooms, plots and screens.
About the Rectangle Area & Perimeter
The Rectangle calculator gives the area, perimeter, diagonal and aspect ratio of any rectangle or square from its two sides, in the unit you choose, with the area also in square metres and square feet. A flooring card adds an allowance for cutting and waste.
What you can do with the Rectangle Area & Perimeter
- Four results: Area, perimeter, diagonal and aspect ratio.
- m² and ft²: Area in both, whatever unit you type in.
- Flooring card: Adds a waste allowance for tiles or flooring.
- Squares too: Works for any rectangle or square.
What each result is for
Area is the space inside, for flooring, paint coverage or land size. Perimeter is the distance around the edge, for skirting boards, fencing or borders. The diagonal is the corner-to-corner distance, useful for checking a room is square or a screen size.
Estimating materials
When buying flooring or tiles, add about 10% to the area for cutting and waste, more for diagonal patterns. Use the slider to set the allowance. Keep both measurements in the same unit; mixing feet and inches is the most common cause of wrong answers.
Screens are measured diagonally
TV and monitor sizes are the diagonal in inches. A 16:9 screen with a 55-inch diagonal is about 48 inches wide and 27 inches tall, enter those to check.
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Frequently Asked Questions
How do I calculate the area of a room in square feet?
Pick ft, enter the length and width, and read the area. A 12 × 10 ft room is 120 sq ft.
Does it work for squares?
Yes, just enter the same value for both sides.
Can I get the area in square metres?
Yes. It's shown in m² and sq ft whatever unit you measured in.
How do I calculate the perimeter of a rectangle?
Add the width and length and multiply by 2: perimeter = 2 × (width + length). A 12 × 10 ft room has a perimeter of 44 ft, which is the length you would need for skirting, a border or fencing around it. The tool shows it right below the area.
How do I convert square feet to square metres?
Divide square feet by 10.7639, since 1 m² equals about 10.7639 sq ft. So 120 sq ft is about 11.15 m². You don't need to do this by hand here, because the tool always shows the area in both m² and sq ft, whatever unit you typed the sides in.
How do I find the area of a plot in gaj or square yards?
In many parts of India one gaj means one square yard, which is 9 sq ft or about 0.8361 m². Pick the yd unit and enter the plot's sides in yards to get the area in yd², or enter them in feet and divide the sq ft result by 9.
How much extra flooring or tile should I buy for waste?
Around 10% extra is common for a simple rectangular room, and more for diagonal layouts, patterned tiles or rooms with many corners. Set the slider on the flooring card between 0% and 25%; a 120 sq ft room with 10% added needs about 132 sq ft.
How many tiles do I need for a room?
Take the area with waste from the flooring card and divide it by the area of one tile, then round up. For a 120 sq ft room with 10% waste, that is 132 sq ft; with 2 × 2 ft tiles (4 sq ft each) you need 33 tiles.
How do I find the diagonal of a rectangle?
Use Pythagoras' theorem: diagonal = √(width² + length²). A 12 × 10 cm rectangle has a diagonal of about 15.6205 cm. This is handy for checking a room is square, since both diagonals should match, or for working out a TV or screen size.
What does the aspect ratio result mean?
It is the width compared with the length, reduced to the simplest whole numbers. A 12 × 10 rectangle gives 6 : 5, and 1920 × 1080 gives 16 : 9, the usual widescreen shape. It tells you the shape of the rectangle regardless of its size.
What if my two sides are measured in different units?
Convert them to the same unit before entering them, because the tool uses one unit for both sides. If a room is 12 ft 6 in wide, enter 12.5 ft, since 6 inches is half a foot. Typing feet in one box and inches in the other gives a wrong area.
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