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Jun 27 · 6 min read

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3 Charts That Explain the Relationship BetweenAd Sizes and Your Campaign’s Performanceby Scott Raynor on Jun 27, 2016

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

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 theyperform — R.I.P. the 468×60. For a more detailed answer, we’ve pickedapart data from our network of more than 25,000 advertisers to explore howour recommended ad sizes perform.

A note on automatic performance tuning

AdRoll recommends our advertisers upload multiple versions of each of oursix recommended ad sizes, as it allows our ad placement algorithm to testand prioritize those that get the most clicks and conversions. This meansthat in order to take advantage of various ad sizes’ competitive advantage,

AdRoll advertisers don’t need to manually track the performance of each adsize.

On to our findings:

Larger ad sizes are recommended because theyperform better

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

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

These larger ads perform better simply because they’re more likely to beseen and therefore clicked on. Additionally, these sizes can benefit frombeing placed above the fold — in the more prominent upper half of thescreen — and are often placed on the sites of premium publishers, whoseaudiences typically perform better.

Also:

Larger ads aren’t just more clickable; they are more likely to get moreconversions 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 convertafter clicking. (Conversions are defined as a user completing a desiredaction, like signing up for a newsletter, creating a login, or making apurchase.)

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

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

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 ofeach user.

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

A variety of sizes is required to reach everycorner of the internet

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 forgrabs in online ad auctions, which start and end in the milliseconds before aweb 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’tguarantee your ads will be seen as far and wide as you desire. There aren’tenough of the large placements available for an advertiser to get the reachthey require.

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

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

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

Dimensions: 970×250 pixels

CTR over Medium Rectangle: 105%

CTCR over Medium Rectangle: 78%

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

Half Page

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 tomaintaining a low cost-per-click.

Medium Rectangle

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Dimensions: 300×250 pixels

Share of Google AdX Inventory: 34%

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

Leaderboard

Dimensions: 728×90 pixels

Share of Google AdX Inventory: 14.8%

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

Wide Skyscraper

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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-conversionrate.

Mobile Leaderboard

Dimensions: 320×50 pixels

Share of Google AdX Inventory: 29%

The mobile leaderboard is the most popular mobile-exclusive ad size. Thisad 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 wecan’t predict which rising ad sizes will be ubiquitous in the future. However,as publishers are increasingly paying attention to the quality of the contentthey host, they’re also looking for ad size and ad creative that complementthis increased focus on quality.

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