Viewability Debunked: Industry Trends and Tips for Optimization

April 16, 2019

If you’ve been following our blog you may have noticed we mention viewability quite often and for good reason. It’s become one of the key factors for evaluating inventory, which is hardly a surprise considering that the purpose of ads is above all to be seen. The advancements in technology now allow for much more precise tracking of this metric than ever before which has definitely been well received by advertisers overall. On the other hand, for publishers, the topic of viewability has been a rather controversial one and has led many to change their long-established practices completely. Having a precise record of an ad’s on-screen time has its pros as well, but it’s definitely taken a toll on media owners and has changed things irreversibly for both programmatic and direct sales.

Defining the Terms

Before we delve into all of its intricacies, let’s start with what viewability stands for and how it’s measured. On the surface it seems pretty simple – viewable ads are the ones that are being seen by the user. However, why and how this data is collected can be less clear. There is still some diversity in definitions in the industry, but the majority of mainstream platform follow the Media Rating Council (MRC) established method, which is that an ad, which has at least 50% of its pixels in view for a minimum of 1s (or 2s for video), is regarded as viewable. In other words, you’d want at least half the ad to be on the user’s screen for a second or more. If you’re still struggling to understand how it works, feel free to check this live demo provided by Google, which illustrates the tracking process.

There are two important distinctions to make here in regard to in-view time measurement. As already mentioned, ads are considered viewable after 1 second of screen time, however, the entire period for which the placement has been in view is being recorded as well. The average percentage of viewable impressions and the average viewable time are two separate metrics, both of which contribute towards the overall inventory quality. For example, having 90% of an ad spot’s impressions being viewable for 2 seconds may hold less merit to advertisers than 70% at an average of 8 seconds. Striking the balance between the two is essential for successful optimization.

The other noteworthy part of the formula is that the ads’ screen time is cumulative, which means that the 1-second timer doesn’t reset each time the ads are sent out of view, but instead is recorded over the entire visit.

With that out of the way, let’s have a look at the primary factors affecting viewability and the best practices you can employ to boost your score.

1. Industry trends

Your placements’ viewability scores can vary based on the vertical you’re in, your audience’s GEO spread, ad types and mediums used, etc. For example, certain content categories seem to come along with higher rates, such as gaming, tech, and entertainment. While this information may not be that useful to most publishers, that are already established in their respective fields, it’s advisable to research and be aware of the average in your segment so that you can evaluate if you’re doing well.

Devices also seem to impact on-screen time significantly, with mobile taking the lead as of late with the increasing amount of engagement portable platforms have been getting. Thus, taking a tailored approach and optimizing for mobile is most likely to be a worthwhile investment of resources for most publishers.

2. Positioning

It’s really a no-brainer but the position of ads plays a huge, if not the largest role when it comes to viewability rates. ATF and BTF placements have been part of publishers’ vocabulary for a while now, but as we enter into this stage of cutting-edge tracking, those terms have become somewhat insufficient to describe a comprehensive strategy. There are so many variables to take into account, especially considering how different website designs facilitate different experiences and engagement. If you’re interested in a more detailed guide on how to approach layout optimization you can check our full post on the subject, but for now, let us give you the cliff notes:

  • ‘Hotspot’ – this is the exact place on a web page that has the highest viewability rate on average. Reports suggest that this is right on the ATF-to-BTF threshold but don’t take that at face value, as this is usually the case for traditional website templates but it may not be so for you. Analyze the elements you have active, where they’re placed and their size, in order to find out where most of your users would be looking at immediately after landing on the page.
  • ATF vs BTF – Above the fold ads hold significant value, even if those are not optimal for viewability. Some advertisers are still targeting such specifically and paying excellent rates for them, so don’t abandon ATF just yet. Below the fold inventory is also not to be underestimated and in some cases, it’s even possible for placements lower on the page to almost match the revenue generated by ATF ones. In general, we advise publishers to think outside the box of traditional placement categories and configure their ad layout based on data and a fair bit of experimentation.
  • Ad stacking – to put it simply, you should always avoid putting a lot of ads close to each other. For one, platforms have a way of detecting that, which leads to a decrease in CPM overall, but it can also harm viewability. Users see ads as a consequence of engaging with content, so having a large block filled with banners often leads to consumers quickly scrolling off, leaving all the placements off the screen. One of the best ways to prevent that is to keep ads alongside content, instead of alternating between the two, and maintain an average of one ad spot per viewable area. The exception would be your top positions, where you may add an additional placement or two to maximize your high-value inventory.
  • Sticky ads – these are rather situational, but as you can imagine they provide the highest scores of all. The downside of such, however, is that they usually replace other static placements, which is why it’s important to weigh the yield of increased viewability against the resulting inventory loss before deciding whether or not to implement these.

3. Ad Sizes

Most publishers would usually be dealing with a small variety of ad sizes on the whole, but fluctuations in viewability are still to be expected within those. Reports show that vertical sizes tend to have the highest screen time, which is not surprising considering that they accompany the largest amount of content. On the other hand, horizontal sizes have the highest viewability rates since it’s really easy to get at least 50% of their pixels on the screen.

There’s plenty of evidence that suggests that, in general, bigger ads are better, however, that may not always bring optimal profits. For example, 320×50 ads on mobile have one of the best viewability rates and average viewable times, as they barely push any content away and with only 50 pixels in the vertical, it would be a challenge to display less than half of them even if you tried. At the same time, the demand for such is not as saturated as it is for, say, 300×250 banners, since smaller size is just not as engaging, thus not generating as many conversions as the alternatives.

With all of this in mind it may be quite confusing what ad sizes you should be utilizing, but not to worry – there’s an upside. Having all of these available are simply tools you can take advantage of, instead of trends you absolutely have to follow to succeed. Always pick the ads that best fit your layout and match your users’ behavior to what each size brings to the table. Viewability is above all a byproduct of engagement, so your primary focus should be on the user experience at all times.

4. Speed

There’s a lot of things that need to happen on the back end before ads can appear on the screen, which is often overlooked when talking about viewability. With asynchronous loading, content is delivered independently from ads, often way before the auctions are completed and the creatives served. This certainly has great benefits for publishers, but it can also harm their viewability rates if neglected. A heavy programmatic setup with multiple bidders and tiers chained together can take a long time to process, which can result in users navigating away from the area before an ad has even had the chance to appear.

One method that has proved to successfully prevent such issues is to have separate setups for each ad placement and optimize them based on position. In a nutshell, the ad spots that load first on the page should feature more streamlined auctions and waterfalls, making sure that banners can appear on the user’s screen as soon as possible. For placements further below, the margin for error is much larger, so heavier setups with increased competition, multiple bidders and tiers are acceptable, as it takes a while for users to reach those areas anyway.


The importance of viewability has been without a doubt on the rise, especially with more and more advertisers discovering traditional action-based models to be less effective. The industry is still shifting and we’re yet to see how marketers will respond to these changes long-term, but in the current state of affairs, it’s safe to say that optimizing for viewability is an absolute necessity for monetary success. We’ve seen plenty of publishers struggle with the concept, always wondering if they’ve made the right choice and whether or not they’re leaving money on the table. Through numerous case studies, experimentation, and data analysis, our team at PubGalaxy has already done the heavy lifting, allowing our clients relief from all that hassle.

If you’re having doubts about your own success with viewability, feel free to drop us a message and request a custom analysis by one of our experts.

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