...
Ad density is calculated by summing the heights of all ads within the main content portion of a mobile page and dividing by the total height of the main content area.
Or, simply: Ad Density = Height of Ads / Total Height of Main Content AreaThe main content of a webpage is the core material that serves the page's purpose and fulfills its primary goal. It excludes headers, footers, navigation menus, and related articles.
For mobile devices, ad density should not exceed 30% of the vertical height of a page.
...