Sales Presentation (5)

Ad sizes don’t make for gripping water-cooler talk—even at AdRoll—but they have a tremendous impact on the performance and reach of all display advertising campaigns. Over the last few years, we’ve changed our recommended ad sizes to encourage a bundle that best balances reach and performance.

But how did we arrive at this mix? And why does it keep changing?

In short, because ad unit sizes impact and influence audiences differently, and their availability rises and falls with our understanding of how well they perform—R.I.P. the 468×60. For a more detailed answer, we’ve picked apart data from our network of more than 25,000 advertisers to explore how our recommended ad sizes perform.

A note on automatic performance tuning

AdRoll recommends our advertisers upload multiple versions of each of our six recommended ad sizes, as it allows our ad placement algorithm to test and prioritize those that get the most clicks and conversions. This means that in order to take advantage of various ad sizes’ competitive advantage, AdRoll advertisers don’t need to manually track the performance of each ad size.

On to our findings:

Larger ad sizes are recommended because they perform better

AdRoll - How Ad Size Influences display advertising

Click-through rate and the rate at which ad viewers convert after clicking, by ad size, from smallest to largest size.

The average click-through rate (CTR) of our two newest recommended ad sizes—the billboard and the half page—is more than double that of the most common ad size: the 300×250-pixel medium rectangle.  

These larger ads perform better simply because they’re more likely to be seen and therefore clicked on. Additionally, these sizes can benefit from being placed above the fold—in the more prominent upper half of the screen—and are often placed on the sites of premium publishers, whose audiences typically perform better.

Also:

Larger ads aren’t just more clickable; they are more likely to get more conversions after each click

On top of higher click-through rates (CTR), larger ads have a greater click-to-conversion rate (CTCR), which is the percentage of users who convert after clicking. (Conversions are defined as a user completing a desired action, like signing up for a newsletter, creating a login, or making a purchase.)

This means that larger ad sizes don’t just get more people to click, but also get even more people to convert after they click.

Larger ads come at a greater cost but maintain a healthy return on investment (ROI)

AdRoll - How Ad Size Influences Your Campaign-03

Relative cost of six AdRoll recommended ad sizes, from smallest to largest.

Larger ads are more expensive. Their average cost per thousand impressions (CPM) is typically higher, meaning it costs more to get large ads in front of each user.

But because viewers of these impressions are so much more likely to click and convert, their overall cost per click (CPC) falls in line with those of smaller ad formats.

A variety of sizes is required to reach every corner of the internet

Ad availability by ad size

Availablity of six AdRoll recommended ad sizes, from smallest to largest.

Ad inventory is essentially the amount and type of ad space that’s up for grabs in online ad auctions, which start and end in the milliseconds before a web page is loaded. And there are constraints on the availability of high-quality ad placements.

This means simply relying on these high-performing ad sizes won’t guarantee your ads will be seen as far and wide as you desire. There aren’t enough of the large placements available for an advertiser to get the reach they require.

Websites tend to have more inventory available in the smaller sizes because these are easier to build into most web pages.

This means having a range of popular ad sizes guarantees you’ll get more opportunities to show off your ad. The leaderboard, medium rectangle, wide skyscraper, and mobile leaderboard, for example, make up 80% of all ad inventory on the web.

Our six recommended ad sizes (and why we recommend them)

Billboard

Billboard_970x250

  • Dimensions: 970×250 pixels
  • CTR over Medium Rectangle: 105%
  • CTCR over Medium Rectangle: 78%

The billboard is our newest recommended ad size. Its premium placement has given it the highest CTCR of all our ad sizes.

Half Page

Half Page Ad Format—300x600 pixels

  • Dimensions: 300×600 pixels
  • CTR over Medium Rectangle: 253%
  • CTCR over Medium Rectangle: 37%

The half page is another large ad size popular on premium publishers’ websites. It maintains one of the highest CTR and CTCR, in addition to maintaining a low cost-per-click.

Medium Rectangle

Medium Rectangle Ad Format: 300x250 pixels

  • Dimensions: 300×250 pixels
  • Share of Google AdX Inventory: 34%

The medium rectangle is the single most popular ad size on the internet. If you upload only one ad size, make it this one (but we don’t recommend that).

Leaderboard

Leaderboard Ad Format: 728x90 pixels

  • Dimensions: 728×90 pixels
  • Share of Google AdX Inventory: 14.8%

 

The standard leaderboard sits in prime ad real estate. It is placed above the fold, in the upper half of the screen. It also displays well on mobile devices.

Wide Skyscraper

Wide Skyscraper: 160x600 pixels

  • Dimensions: 160×600 pixels
  • Share of Google AdX Inventory: 6.9%

 

The wide skyscraper’s tall dimensions make it viewable while users scroll, and it’s the third-most used size. It also boasts a high click-to-conversion rate.

Mobile Leaderboard

Mobile Leaderboard: 320x50 pixels

  • Dimensions: 320×50 pixels
  • Share of Google AdX Inventory: 29%

 

The mobile leaderboard is the most popular mobile-exclusive ad size. This ad size helps your ads stay visible as users move across devices.

What’s next in ad sizes?

Trends in ad sizes depend largely on the digital publishing industry, so we can’t predict which rising ad sizes will be ubiquitous in the future. However, as publishers are increasingly paying attention to the quality of the content they host, they’re also looking for ad size and ad creative that complement this increased focus on quality.

That means good ads, in bigger and more prominent positions, will likely prove more effective.

For those daunted at the thought of making new ads, check out our help center article on creating successful ads, or use our Design Squad, which creates ads for AdRoll customers, for free.