Rectangle Calculator
Calculate the area, perimeter, diagonal, and aspect ratio of a rectangle from its length and width, or solve sides from area and perimeter.
Rectangle dimensions
Area
12
- Length
- 4
- Width
- 3
- Perimeter
- 14
- Diagonal
- 5
- Aspect ratio
- 1.3333
Frequently Asked Questions about the Rectangle Calculator
How do you calculate the area of a rectangle?
Multiply length by width: A = L * W. If your sides are in inches, area comes out in square inches. Keep both inputs in the same unit and the result stays consistent.
What is the formula for the diagonal of a rectangle?
Apply the Pythagorean theorem to the two sides: d = sqrt(L^2 + W^2). For a 4 by 3 rectangle the diagonal is sqrt(16 + 9) = 5. For a square with side s, the diagonal is s * sqrt(2).
Can I solve a rectangle from area and perimeter alone?
Yes, when a real solution exists. Length and width are the two roots of x^2 - (P/2) x + A = 0. The discriminant is (P/2)^2 - 4A. If it is negative, no rectangle has that combination of area and perimeter.
Why does area = 100 with perimeter = 20 return no result?
A perimeter of 20 means L + W = 10, so the largest possible area is the square case 5 by 5 = 25. Asking for an area of 100 is impossible at that perimeter, so the discriminant goes negative and the calculator reports no solution.
What is the aspect ratio?
Aspect ratio is length divided by width. A square has aspect ratio 1. A 16 by 9 widescreen rectangle has aspect ratio about 1.778. Use it to compare rectangle shapes regardless of size.