A computer screen uses millions of pixels to display images. These pixels are arranged in a grid horizontally and vertically. The number of pixels horizontally and vertically is shown as the screen resolution. Screen resolution is typically written as 1024 x 768 (or 1366 x 768 or 1920 x 1080). This means that the screen has 1024 pixels horizontally and 768 pixels vertically.
When building a website, the de facto width is 960px. We’d assume that it would be more due to the increasing size and resolutions of our computer screens but even people who uses large monitors tend to keep their browser less than 1024px, which is the standard full screen, so that they could run other applications or browsers at the same time. Another reason why the de facto width is 960px is because of line length. It is said that if a line of text is too long, it becomes less readable therefore having a wider width will only promote more empty/white space.
In today’s world, there is a tremendous increase in mobile usage. With that being said, a lot of websites are made available in mobile-optimized versions – also known as mobile responsive websites. Hence, there is really no need for an extremely large width. For web developers and designers who are creating websites should include popular mobile devices during ‘browser testing’ to make sure that the designs and layouts are well adjusted. At the end of the day, no matter what you are designing, the needs of your client and their target audience should be the driving force behind your decisions.