When choosing your ad size, you have multiple options, but what are the best ones to use and why?

According to the official Adsense website, these are the top performing ad sizes:

On desktop:

• 336×280 large rectangle
• 300×250 medium rectangle
• 728×90 leaderboard
• 300×600 half page

On mobile:

• 320×100 large mobile banner

Aside from those, there are many other sizes, but the nice thing about the above is that there are many more advertisers targeting those sizes, meaning more competition, meaning more revenue for you. Since those are the standard, ad designers tend to create banners in those sizes first.

The people at Labnol have compiled the following chart where you can see the average CTR for each size:

Also, in general (although this rule is not 100% accurate), wider sizes tend to get a higher CTR (since, well, they are bigger, thus more noticeable).

Those sizes have been tested across multiple websites and seem to be the winners, but as always, there is room for testing.

Bear in mind that size is just one part of the equation. Placement is at least as important as the size you choose