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Quik Calculate

Calculate diagonal, area, perimeter, and angles instantly.

Diagonal of a Rectangle

A rectangle is a quadrilateral with four right angles. The diagonal is the straight line connecting opposite corners. Every rectangle has two diagonals of equal length that bisect each other.

l w d α

How It Works

Calculation Flow

  1. Input Values

    Enter your measurements

  2. Apply Formula

    Pythagorean theorem applied

  3. Calculate

    Instant computation

  4. Display Result

    View your results

How to Find the Diagonal of a Rectangle?

To calculate the diagonal (d), you can use the Pythagorean theorem if you know the length (l) and width (w):

d = √l2 + w2

Possibilities of Diagonal of Rectangle Measurements

Depending on what information you have ("Given"), the formulas change:

  • Given Side & Area (A): First find the other side (w = A/l), then calculate d.
  • Given Side & Perimeter (P): First find the other side (w = P/2 − l), then calculate d.
  • Given Side & Angle (α): Use trigonometry (w = l × tan(α/2)) to find the missing side.

Practical Example

If a rectangle has a length of 4 cm and a width of 3 cm:

d = √42 + 32 = √16 + 9 = √25 = 5 cm

How to Use a Quik Calculate?

  1. Choose the parameters you know from the dropdown menu.
  2. Enter your values into the fields.
  3. The calculator automatically updates the diagonal, perimeter, circumcircle radius, and area.

In construction and deck building, squaring your layout with diagonal measurements is essential before pouring footings, while a sonotube calculator helps determine the concrete volume needed for cylindrical forms.

Frequently Asked Questions

What is the formula for the diagonal?
The formula depends on the Pythagorean theorem: d = √(width² + height²).
Does diagonal bisect the angles?
No, not in a rectangle (unless it is a square). In a general rectangle, the diagonal bisects the area but not the corner angles.