lammert - 1:13 am on Dec 10, 2010 (gmt 0)

Aspect ratios are not always easy numbers. With the older screen resolutions like 640x480, 800x600 or 1280x1024 it was almost always easy to find a small value for the aspect ratio like 4:3 or 5:4. With the new wide screen displays, especially on notebooks you will sometimes find weird values.

What you have to find is the greatest common divisor [en.wikipedia.org] for the horizontal and vertical pixel sizes. I have two monitors here. The easiest example is my desktop screen which is a 19" 1280 x 1024 version:

1280 x 1024 = 2*2*2*2*2*2*5 x 2*2*2*2*2*2*2*2

The greatest common divisor is 2*2*2*2*2*2, which is 256 and gives an aspect ratio of 5:4.

But some screen sizes are more difficult. My other current screen is a wide screen notebook screen with the size 1366 x 768.

1366 x 768 = 2*683 x 2*2*2*2*2*2*2*2*3

683 is not dividable by 2 or 3. The greatest common divisor of these two screensizes is therefore 2, which gives an aspect ratio of 683:384.