Rectangle Calculator
Enter a rectangle’s length and width to find its area, perimeter and diagonal.
units
units
- 1
Diagonal = √(l² + w²)
√(10² + 6²) = 11.6619Pythagorean theorem: the diagonal is the hypotenuse of the right triangle formed by the two sides. - 2
Perimeter = 2 × (l + w)
2 × (10 + 6) = 32 - 3
Area = l × w
10 × 6 = 60
Formula
How this is calculated
A rectangle is defined by just two numbers: its length (l) and its width (w), the lengths of its two pairs of parallel sides. Because every corner is a right angle and opposite sides are equal, these two inputs fix the whole shape. The calculator reads both values, treats them as the same linear unit you typed (cm, m, ft, in — it is unit-agnostic), and requires each to be a positive number; zero or negative values produce no result.
Area is the surface enclosed by the rectangle, found by multiplying the two sides: Area = l × w, expressed in square units. The perimeter is the total distance once around the edge, Perimeter = 2 × (l + w), since each side appears twice. The diagonal joins two opposite corners and acts as the hypotenuse of a right triangle whose legs are l and w, so by the Pythagorean theorem Diagonal = √(l² + w²).
Results are rounded to four decimals, so irrational diagonals are approximate. The formulas assume a true rectangle with exact right angles and flat sides; they do not apply to skewed parallelograms or curved shapes.
Examples
| Input | Result |
|---|---|
| length = 10, width = 6 | Area = 60, Perimeter = 32, Diagonal ≈ 11.6619 |
About this calculator
A rectangle is a four-sided polygon (quadrilateral) where every interior angle is a right angle and opposite sides are equal in length. Its area is simply length multiplied by width, while the perimeter is the total distance around the shape.
The diagonal connects opposite corners and is found with the Pythagorean theorem, since it forms the hypotenuse of a right triangle made by the length and width. These three measurements cover most practical needs in construction, flooring, framing and design.
Frequently asked questions
Multiply the length by the width. For example, a rectangle 10 by 6 units has an area of 60 square units.
Use the Pythagorean theorem: diagonal = √(length² + width²), because the diagonal is the hypotenuse of a right triangle formed by the two sides.
The calculator is unit-agnostic. Whatever unit you enter (cm, m, ft, in), the area is in square units and the perimeter and diagonal share the same linear unit.
Also known as
TG we-Calculate Editorial Team. (2026). Rectangle Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/rectangle-calculator
TG we-Calculate Editorial Team. "Rectangle Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/rectangle-calculator.
TG we-Calculate Editorial Team, "Rectangle Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/rectangle-calculator
@misc{wecalculate_rectangle_calculator, title = {Rectangle Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/rectangle-calculator}}, year = {2026}, note = {TG we-Calculate} }
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