Best Mobile Ad Sizes for 2021

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In 2018, mobile advertising accounted for an astounding 75% of all digital ad spend, with companies in the U.S alone spending over $70 billion to reach an estimated three billion mobile phone users. Since 2018, the number of mobile users has increased to 5.2 billion, and mobile use continues to grow at a rate of around 2%.

With these kinds of numbers on the board, getting your mobile advertising right is crucial — or you’ll find yourself hemorrhaging ad revenue — and the first step is to pick the correct banner ad sizes.

To help you get the best out of your website ad slots, we’ve compiled the best mobile ad sizes in 2021 for mobile and tablet devices.

Let’s get started by looking at some of the most effective mobile ad sizes.

  • Since Google changed its ad placement policies in 2017, the 300×250 ad has been an exceptionally valuable ad size.
  • The 728×90 leaderboard shouldn’t be overlooked as it is still the largest banner ad unit[7] viewable on tablet devices.
  • If you’re concerned about intrusive ads on mobile, the 320×50 mobile banner is an excellent choice.
  • The recent implementation of Web Interstitials by Google has boosted the appeal of using interstitials especially for 336×280 and 320×480.

Now, let’s take a look at some of the ad sizes you may be missing out on.

300×250: The Workhorse

The 300×250 ad size, also known as the “Medium Rectangle,” has been one of the most popular ad sizes since Google’s revisions to their mobile ad policies in 2017, and we fully expect it to stay that way.

The reason why the 300×250 inline rectangle is so popular is because of its versatility. You can use it with both desktop and mobile web, and its performance[3] is boosted by the fact that you can use it in-article or in-feed. 

On mobile, the 300×250 ad commands a higher CPM[1]. The 300×250 ad is also large enough to support embedded video, while still being small enough to be used multiple times on the same page.

728×90: The Tablet Leaderboard

Because it is so wide, the 728×90 leaderboard can get overlooked in favour of more smartphone-friendly formats. According to research conducted by adpiler, the 728×90 was the third most popular ad size in 2019, making up 12.1% of all ad impressions for the year.

According to Google, the leaderboard tends to have more ad inventory[8][4] available from advertisers, which can increase earnings when both text and image ads are enabled.

320×50: The Least Intrusive

Suppose you are worried about intrusive advertising affecting the user experience of your mobile site. In that case, the 320×50 mobile banner is an excellent compromise between this size’s earning potential and the minimum amount of space given over to ads.

One of the other significant benefits of the 320×50 format is that it is often the first thing the user sees on any mobile website, which is probably why it accounted for 27.7% of all ad impressions in 2019.

336×280 and 320×480: The Interstitial Newcomers

Google’s recently launched web interstitial ads[2] for desktop and mobile have changed how digital publications can approach monetization. Google’s beta partners have seen CPMs of up to $20 on their sites. Interstitial ads serve as transitions, often appearing between pages or between sections of a mobile game.

The greatest benefit of interstitial ads is that they provide full coverage and high viewability[5] compared with banners or native ads[6]. Because they occur at natural transition points, interstitial ads can also provide incremental revenue without harming the overall user experience.

Google’s web interstitial ads support three sizes; in addition to the ever-popular 300×250 inline rectangle, the 336×280 and 320×480 are two ad sizes to watch in 2021.  

1. Cost Per Mille/Thousand [CPM] ( CPM ) Cost per mille, or thousand (mille = thousand in Latin). A pricing model in which advertisers pay for every 1000 impressions of their advertisement served. This is the standard basic pricing model for online advertising. See also CPC and CPA.
2. interstitial ads. Interstitial ads are full-page ads that tend to serve during transition points within a web page or mobile app. The ads are loaded in an iframe that displays over the content of the current app or page.
3. performance. A form of advertising in which the purchaser pays only when there are measurable results.
4. ad inventory. Ad Inventory refers to the number of ad impressions available for sale on a publisher’s website or mobile app. In other words, these are the commodities available for the advertisers to buy on the website.
5. viewability. Viewability relates to the amount of time a user saw an ad.

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