📐 Rectangle Area Calculator
Enter the width (a) and height (b) of a rectangle to calculate its area, perimeter, and diagonal.
Rectangle Formulas
Area = a × b
Perimeter = 2 × (a + b)
Diagonal = √(a² + b²)
Worked Examples
A 4 x 6 rectangle has an area of 24, a perimeter of 20 and a diagonal of √52 ≈ 7.2111.
A square is a rectangle with equal sides, so 5 x 5 gives area 25, perimeter 20 and diagonal ≈ 7.0711.
What the Result Assumes
All three values are exact for a perfect rectangle with straight sides and right angles. Results keep the unit you type (metres in, square metres out) and are rounded for display only; diagonals are irrational in most cases and cannot be written exactly as decimals.
Frequently Asked Questions
- Why is the diagonal longer than either side?
- The diagonal is the hypotenuse of the right triangle formed by the two sides, so it equals √(w² + h²) and is always longer than the longer side.
- How do I find the width from area and height?
- Divide the area by the height. From a perimeter, use width + height = perimeter / 2 and solve for the missing value.
- Is a square a rectangle?
- Yes, a square satisfies every property of a rectangle with the extra condition that all sides are equal - the rectangle formulas apply unchanged.