Rectangle Calculator
Enter the length and width of a rectangle. For a square, enter the same value twice.
Result
- Diagonal
- 9.434 cm
- Length to width ratio
- 1.6
Formula
- Area = length × width
- Perimeter = 2 × (length + width)
- Diagonal = √(length² + width²)
How the Rectangle Calculator works
A rectangle has four right angles and two pairs of equal sides. Its area is the product of two adjacent sides and its perimeter is the total length of all four.
The diagonal splits the rectangle into two right triangles, so its length follows from the Pythagorean theorem. Measuring both diagonals is the standard way to check that a frame is square: they must be equal.
Worked example
An 8 cm by 5 cm rectangle has an area of 40 cm², a perimeter of 2 × 13 = 26 cm and a diagonal of √(64 + 25) = 9.434 cm.
Frequently asked questions
How do I find the width from the area and length?
Divide the area by the length. A 40 square unit rectangle that is 8 long is 5 wide.
What is the diagonal of a square?
The side times √2, about 1.4142. A 10 unit square has a diagonal of 14.142.
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