Use Banner Ads Effectively
According to Google AdSense, the most effective banner ad sizes that can be hosted on a publishing site are:
728×90px — Leaderboard
300×600px — half page
300×250px — medium rectangle
336×280px — large rectangle
The following are just examples of how these ad sizes are actually being used:
Image credit: Forbes
Image credit: BuzzFeed
Image credit: Obsev
The main reason the ad sizes above work is because most advertisers design their ads for these sizes. In short, you will get the Latest Mailing Database most competition on your website, which will lead to higher CPCs.
Since publishers themselves decide ad sizes first, you should consider using the suggested sizes in your web layout. Choose one of the most effective ad sizes for your layout and even get up to 100,000 advertisers actively bidding on those sizes.