Density rule. Web Designer Knowledge Base
In order to successfully choose a grid, you need to understand how much different information there will be on the site.
For a promo page with a couple of large headlines and large photos, a grid in 4 columns, or even two, is suitable. And for a loaded news site with a bunch of articles, news, widgets and banners, you will need 8-12.
The right choice will save you, on the one hand, it will need to push large blocks into too small a grid, and on the other hand prevent the appearance of a variety of "holes" if the grid was too large and the information is too much.
The feeling of the created site design depends directly on the density the grid and the information in it: you can get a rich information site , or maybe a spacious and airy presentation site.