Rectangle Area Calculator

Formula

A = b × h

Area of a rectangle: formula and worked example

A rectangle is a four-sided shape with four right angles, where each pair of opposite sides has the same length. To get the area you multiply base by height: A = b·h. Take b = 6 m and h = 4 m and the area comes to 24 m². The perimeter is P = 2(b + h), and for the diagonal you lean on Pythagoras: d = √(b² + h²). Same example, d = √(36 + 16) = √52 ≈ 7.21 m.

Where the rectangle shows up in practice

Floors, walls, screens, doors, windows, and almost every paper size you handle. When you are painting or tiling a wall, tack on a 10% safety margin for cuts and waste. Paper is a neat case: the A-series (A0, A1, …, A4) keeps a fixed ratio of √2 between its sides. Fold an A4 in half and you get an A5 with exactly the same proportions, which is why layouts and margins scale so cleanly from one size to the next.

Then there is the golden rectangle, prized for its looks, with sides in the ratio b/h = φ ≈ 1.618 (the golden ratio). You meet it again and again in classical architecture (the Parthenon facade), in Renaissance painting and in modern logo work. Its quirk: slice off a square and what remains is a smaller golden rectangle, a shape that keeps repeating itself.

FAQ

What if I know the area and one side? Divide one by the other. The side you are after is A / b or A / h. So a 24 m² rectangle with a 6 m base works out to a 4 m height.

Do I have to subtract doors and windows when painting a wall? With ordinary openings you can usually let it slide. But if you are dealing with a big window or door, take its area out of the total so you do not end up buying paint you will never use.

What is the difference between a rectangle and a parallelogram? A parallelogram has its opposite sides parallel, but the angles can be anything. Make all four of those angles 90° and the parallelogram becomes a rectangle.