Skip to content
Math & Statisticsgeometry

Rectangle and Square Calculator

Every measurement of a rectangle from its two sides, including the diagonal and the simplified aspect ratio. The diagonal is Pythagoras, which is why a 16:9 screen is measured across the corner.

Also called: rectangle area and diagonal.

Area
48

Area 48, perimeter 28, diagonal 10. The aspect ratio is 1.33, which simplifies to 4 : 3.

Perimeter
28
Diagonal
10
Aspect ratio
1.33
Simplified ratio
4 : 3
Side of a square with the same area
6.93
How this is calculated
Method and background

How this is calculated

Area and perimeter are multiplication and addition. The diagonal is the hypotenuse of the two sides, which is how screens and panels are specified. The aspect ratio in lowest terms is what tells you whether something is 4:3 or 16:9, and the equivalent square side shows how much of the perimeter is being spent on shape rather than area.

the diagonal comes from Pythagoras on the two sides
l
Length
w
Width

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

an eight by six rectangle

Length
8
Width
6

Area48

A 6-8-10 triangle, so the diagonal is exactly 10

Open this example

Method and limits

What it assumes

  • A true rectangle with right angles.

What it deliberately does not model

  • The simplified ratio rounds the sides to whole numbers first.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why are screens measured diagonally?
Convention, and it flatters. A 27 inch diagonal at 16:9 is only about 23.5 inches wide, and two screens with the same diagonal in different aspect ratios have different areas.