Rectangle Calculator
Enter the length and width of a rectangle to get its area, perimeter and diagonal. Every result is computed at full precision and displayed to your chosen number of decimal places.
Enter dimensions
Enter length and width, then press Calculate.
Rectangle formulas
Area: A = length × width
Perimeter: P = 2 × (length + width)
Diagonal: d = √(length² + width²)
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Frequently asked questions
Functionally none — both are sides of the rectangle. Conventionally length is the longer side, but the calculator treats them symmetrically.
The diagonal splits the rectangle into two right triangles, so you use the Pythagorean theorem: d = √(length² + width²).