Calculate the diagonal of any rectangle quickly using this online tool empowered by the Pythagorean theorem. Enter the width and height, choose your preferred units, and get an instant result. A live diagram shows the diagonal in red, labeled as c, between sides a and b.

Rectangle Diagonal Calculator

a b c

Enter the width and height of the rectangle to calculate and visualize its diagonal.

Width (a)

Height (b)

Decimal Places

Diagonal (c)

Calculation process will appear here.

How to Use the Rectangle Diagonal Calculator

This tool supports inputs in meters, centimeters, or inches, and allows you to specify the number of decimal places for precision. Ideal for geometry tasks, construction planning, or design calculations.

  1. Enter Width (a): Type the rectangle’s width and select its unit (m, cm, or in).
  2. Enter Height (b): Type the rectangle’s height and select its unit.
  3. Set Decimal Places: Choose how many decimals you want in the result (default is 2).
  4. Select Output Unit: Choose the unit in which to display the diagonal result.
  5. Click Calculate Diagonal: The diagonal (c) will appear below, with step-by-step calculation and a visual representation.
  6. To Reset: Click “Clear All” to start a new calculation.

Famous Rectangles and Their Diagonals

Here are notable rectangular objects with real-world dimensions and their diagonals calculated using the Pythagorean theorem:

  • A4 Paper – 21.0 cm × 29.7 cm → Diagonal: 36.44 cm
  • Credit Card (ISO/IEC 7810 ID-1) – 85.60 mm × 53.98 mm → Diagonal: 101.60 mm
  • US Dollar Bill – 6.14 in × 2.61 in → Diagonal: 6.67 in
  • iPhone 14 (Display) – 2.53 in × 5.48 in → Diagonal: 6.04 in
  • MacBook Air 13.6″ (Screen) – 11.76 in × 7.35 in → Diagonal: 13.60 in
  • LEGO Brick 2×4 – 31.8 mm × 15.8 mm → Diagonal: 35.59 mm
  • iPad Pro 12.9″ (Screen) – 7.73 in × 10.32 in → Diagonal: 12.91 in
  • US License Plate (Standard) – 12 in × 6 in → Diagonal: 13.42 in
  • Nintendo Switch (Console) – 9.4 in × 4.0 in → Diagonal: 10.27 in
  • NBA Basketball Backboard – 72 in × 42 in → Diagonal: 83.89 in

Need any extra features in this tool? Let us know in the comments!

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