Given dimensions of an image, determine aspect ratio to create specifications.

Some common aspect ratios include 4:3 and 16:9.

A 4:3 aspect ratio means that for every four units of width, there are three units of height. The same applies for the 16:9 aspect ratio - for every sixteen units of width, there are nine units of height.

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Aspect Ratio Formula

The formula for finding aspect ratio is:

AR = W / H


  • AR is the aspect ratio
  • W is the width of the displayed image
  • H is the height of the displayed image

Note that W and H are measured in inches or millimeters.

There is another useful way to describe an aspect ratio. If you take the 4:3 aspect ratio and divide 4 by 3, the result is 1.33. Therefore, you could alternately describe the 4:3 aspect ratio as 1.33:1, meaning that for every 1.33 units in width, there is 1 unit in height. Again, the same applies for the 16:9. When you divide 16 by 9, the result is 1.78. In the case of the 16:9 aspect ratio, you can alternately describe its aspect ratio as 1.78:1, meaning that for every 1.78 units in width, there is 1 unit in height.

Let's take a couple of common computer display resolutions and discover their aspect ratios. First, look at 1024x768. If you divide 1024 by 768, the result is 1.33, so the 1024x768 computer resolution can be described as having an aspect ratio of 1.33:1. You could also take 1024 pixels in width and divide it by 4 to get 256 (4 units of 256 pixels each) and then multiply one of those pixel units, 256, by 3 to get 768 pixels.

Not all displayed images are 16:9 or 4:3. For example, a common computer resolution is 1680x1050. Dividing 1680 by 1050, gives a result of 1.6. Therefore, the 1680x1050 computer resolution has an aspect ratio of 1.6:1 or 16:10.

This is a slightly different aspect ratio than the 1.78:1 or 16:9 aspect ratio. Even though the difference between 16:10 and 16:9 seems small, you cannot project a 16:10 image onto a 16:9 screen.

Watch the Video: Aspect Ratio

View the video lecture (4 mins) about solving for aspect ratios.

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Quick Tip: Documenting Aspect Resolution

Document the resolution of an image by the horizontal and vertical pixel counts and not by the VESA identifiers (1920x1200 instead of WUXGA).

The width and height of an image can also be used to determine a screen's diagonal measurement using the Pythagorean Theorem.

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Screen Diagonal Formula (Pythagorean Theorem)

The diagonal of a screen can be calculated using the Pythagorean Theorem:

 A2+ B2 = C2


  • A is the height of a screen
  • B is the width of a screen
  • C is the diagonal length of a screen
Watch the Video: Solving the Pythagorean Theorem

For information on solving the Pythagorean Theorem, view the video lecture. (3 mins)