Table of contents
Ad Viewability is a key factor affecting the price that advertisers are willing to pay for your ad inventory, making viewability one of the few levers that publishers have to influence bid rates. A 1% increase in ad viewability leads to an average 2% increase in CPM, giving publishers a valuable and measurable incentive to optimize for viewability.
A 1% Increase in viewability = 2% increase in CPM
Through this deep dive, we aim to share everything that publishers need to know both to understand ad viewability from a publisher perspective and to increase viewability on their ad inventory to earn more. OKO Deep Dives are designed as much as a reference as deep learning materials, so feel free to use the contents list below to jump straight to the relevant section if you are looking for answers to specific questions, or read on for the full story on ad viewability for publishers.
What is viewability?
Viewability is a metric that gives publishers and buyers an indication of what proportion of ads have a realistic chance of being seen (Opportunity To See, or OTS). If an advertiser buys 100,000 impressions that have 50% viewability then they can work on the assumption that around 50,000 of those impressions actually have the chance to be seen by humans. As such, viewability is a metric that deals with the deliverability of impressions rather than real eyeballs or engagement. It’s a measure of “viewability” not “views”.
What counts as a viewable impression?
Of course, no-one is checking which ads users physically see, so ad viewability is measured by how much of an ad is in-view on a user’s screen and how long it stays there. For display impressions (banners, MPUs, etc), an impression is counted as viewable when at least 50% of the pixels are in the viewable part of the user’s screen for a minimum of 1 second.
For video ads, the requirement is slightly different. 50% of the ad still has to be in view, but it has to be playing and remain in view for a minimum of 2 seconds.
These definitions of what is viewable have been set by the Media Rating Council and adopted by the Interactive Advertising Bureau to ensure that a common definition is being used across the digital advertising industry.
Why bother measuring ad viewability?
Back in 2013, media measurement experts ComScore released data showing that 54% of online advertising impressions sold were never seen. The fact that many impressions were never viewed was not much of a surprise to many in the industry, but the data underlines the scale of the issue and brought it to the attention of many involved in advertising who were less familiar with the practicalities of the medium.
Understandably, many brand advertisers were unhappy that less than half of the advertising they were buying was ever seen and ad viewability scoring was offered as a way of addressing the issue; giving buyers more insight into what they were buying and opening up the opportunity to bid for viewable impressions.
What makes an impression unviewable?
If only half of ad impressions are ever seen, you might rightly wonder what happens to the remainder. The classic example of a low-viewability placement is an ad that appears low down in a long article. It is perfectly valid for a publisher to place ads low down on long pages, but viewability will be affected if all users don’t scroll through the whole article and reach the ad unit.
Low ad viewability isn’t exclusive to “Below the fold” units though. Many publishers use masthead units Above the Fold, believing that these will score as highly viewable. It might be surprising to know that such placements can score poorly, particularly if they are slow loading or if the website/app design encourages users to scroll down quickly to reach the content. Because ads need to load and remain in view for 1 second, users can have scrolled the ad off-screen before the impression counts as viewable.
For video impressions, the cause could be as simple as the user stopping the video, or hitting the back button when the ad is presented and before the required 2 seconds has elapsed.
We’ll give more specific examples later in the guide when we talk about optimizing for viewability.
Why should publishers care about viewability?
It’s easy to think of ad viewability as a metric that only concerns advertisers and buyers. Equally, many publishers see viewability scores as being another tool that buyers can use to squeeze rates ever lower. Whatever your thoughts on that, the reality is that buyers are definitely using viewability when booking their spend.
Publishers with low viewability will be overlooked by buyers who set minimum thresholds. Those with higher viewability will not only be considered, but can justify a premium. Ensuring strong viewability helps secure higher bids and more demand for your inventory, so is very much a concern for publishers looking to improve their revenue.
Viewability vs Active View
Publishers who monetize with Google AdSense or Google Ad Exchange may be more used to seeing the term “Active View” rather than “Viewability”. Active View is Google’s proprietary way of measuring ad viewability. There are many different providers with slightly different ways of assessing viewability. Although different providers all use the IAB definitions to determine what is viewable, the way they measure that can differ. Active View is Google’s method, but in most contexts can be used as a synonym for viewability.
Should AdSense publishers worry about active view and viewability?
As AdSense pays publishers by the click rather than by the impression, viewability might seem less relevant. Whilst it might not be as high a priority as it would be for publishers being paid on a CPM basis, viewability definitely still plays a part for AdSense publishers.
Most immediately, ads cannot be clicked if they are not seen meaning that CTR (which definitely does directly impact AdSense revenue) tends to follow viewability. Publishers looking to improve their CTR (and therefore revenue) can use viewability / Active View as a leading indicator to pursue. This allows for CTR optimization without unknowingly optimising for accidental clicks.
Longer term, improved Active View scores can help support higher yield by highlighting your inventory as being higher performing. This can help attract higher paying placement targeting campaigns as well as stopping your inventory getting blocked by advertisers wishing to avoid poor performing placements.
What is a good ad viewability rate?
Average ad viewability varies by Geography, device type and even by vertical, so it is difficult to give a single benchmark number for publishers to aim for.
Internally at OKO, we score inventory with ad viewability of 70+ as Good, and 80+ as Excellent and certainly see revenue improvements in line with that. How realistic those targets are for each individual publisher is a more nuanced discussion.
What is a typical viewability rate?
The table below shows average viewability rates by channel and key Geo for publishers looking for average data to benchmark themselves against. For comparison, YouTube ads offer >90% viewability across all regions.
How to measure ad viewability
There are a number of third-party tools that can be used to measure viewability, but most are aimed at the buy-side of the industry, allowing them to verify the viewability of the impressions that they buy. Most publishers will rely on viewability reporting provided by Google. This is easily available and free to publishers.
Google offers three methods to report on viewability, depending on your set-up. What is most important for publishers is to pick a single method and stick to that. This allows progress to be accurately tracked as viewability optimization is performed:
- Active View Viewable in AdSense : Most useful for publishers who run ads through AdSense alone
- Total Active View % viewable impressions in Ad Manager Historical : Viewability across all of our ad server impressions
- Active view viewable in Ad Exchange Historical : Viewability across Ad Exchange impressions only
How to improve ad viewability
With ad viewability becoming an increasingly important factor affecting publisher earnings, publishers are inevitably looking to optimize for ad viewability. The good news is that most publishers can make an impact on their viewability with some reasonably simple changes. As with many types of optimization, it gets more difficult to find improvements as your viewability scores improve, but the strategies below will increase viewability for most.
Publishers have four categories of improvements they can make to improve their ad viewability scores:
- Design
- Speed
- Content
- Ad Serving
We’ll look at each in turn and give specific tactics that you can work with to improve viewability on your own ad inventory.
Improving ad viewability through design
Design changes are what immediately come to mind for most publishers when we talk about optimizing viewability.
Using Above-The-Fold inventory to increase viewability
The classic example of using design to improve viewability is to move ad units “above the fold”. It’s overly simplistic (and often plain wrong) to say “moving ads up the page increases” viewability, but the aggregate data does certainly demonstrate that “above the fold” inventory still delivers the highest viewability, as the graphic below shows.
It’s important to understand that there is no one “fold” for all users though. With multiple device types, screen resolutions and even browser set-ups to consider, it is impossible to pick a point that represents the fold for everyone.
One solution is to measure scroll depth of users on your website. Understanding how far down your content users scroll allows you to position your ad placements where more users will see them, boosting viewability.
What is an “Above the Fold” ad?
We often talk in terms of ads being Above the Fold (ATF) or Below the Fold (BTF). This is language borrowed from advertising’s origins in print and refers to the fold of a print newspaper. Newspapers are often displayed folded in half, with the top half upmost. This means that any content appearing “above the fold” gets seen more.
Although we don’t fold webpages and app screens, we often do need to scroll down them to view the content. In the digital world, the “fold” is the point where the first screen full of content ends and users have to scroll to see more. Just as in the print world, content “above the fold” is generally seen more and perceived as higher value.
Avoid top of page placements
One sure way to ensure that your ads appear “above the fold” for everyone is to place them at the very top of the page. This seems like an obvious way to improve viewability, but can be counter-productive.
Users have learned to find the content they are looking for in the main body of the page and will often automatically scroll down to the content as the page loads. This is particularly common on mobile devices.
As viewability on display ads is only measured once 50% of an ad has been in view for 1 second, this can mean that the user has scrolled the ad out of view before viewability is recorded. Large headers and slow-loading ads can exacerbate this effect, but it is always worth paying particular attention to the viewability metrics of top of page placements.
Use on-fold and immediately above fold placements
Ad placements that are on, or immediately above the “fold” will, perhaps surprisingly, generally out-perform those higher up the page. According to Google, the most viewable position for an ad unit is immediately above the fold. Users’ attention is often at the bottom of the screen and these placements will remain in view for longer as users scroll down the content.
Placing ads immediately “above the fold” can be challenging though, as screen sizes vary so much.
Aligning ads with the most sticky parts of your content
It’s easy to think of viewability as being a gradient ranging from high viewability at the top of a page to low at the bottom. This might be accurate for some types of text content, but the reality is usually more complex with users scanning through content and then dwelling on the parts that most engage them.
An extreme example of this would be a dry looking article with an engaging looking video unit or image lower down the page. Users might skip through the article quickly then dwell on media, meaning that units aligned near the image or video would be more viewable.
Tools that track where on a page users spend time can be useful to understand which part of a page is most viewable, but they are not essential. Common sense and experience are often enough as it is often obvious where on a will command most users attention.
Short pages lead to higher viewability
It is worth keeping in mind that shorter pages do correlate with higher viewability. It would rarely make sense to shorten content solely with the aim of increasing viewability. But, publishers using multi-page content may be able to find improvements by optimising page lengths with more viewability and page depth in mind.
Improving ad viewability through speed
Both the speed of ad serving & the speed of the website or app itself have an impact on viewability and the revenue that publishers earn. Even a 1 second delay in impressions being served to the user can have a significant impact both viewability and impressions served, (meaning a double hit for publishers as they are serving less and less valuable inventory).
| Impact of 1 second delay | ||
| Impressions | Viewability | |
| Mobile | -1.1% | -3.6% |
| Desktop | -1.9% | -2.9% |
| Source: web.dev – Fast Ads matter. | ||
Use a fast auction wrapper
Header Bidding brings great advantages to publishers in terms of revenue gains, but it does come with overheads in terms of site and ad serving speed. Not all wrappers are equal though and selecting a fast wrapper is one way to minimise the impact on speed.
Publishers with particular sensitivity around speed (be it for reasons of viewability or any other), might consider server-side auction solutions such as Open Bidding. Server-side solutions can obtain bids more quickly from participating vendors, meaning that the auction can run more quickly for the user.
Limit the number of Header Bidders
If you are running Header Bidding client-side (for instance, with Prebid) then each bidder that you add to the auction will have an impact on overall load to the user. More bidders will generally also mean a slower auction.
It can be tempting to add as many bidders as possible to the wrapper, and CPM rates can often support that approach. As more bidders slows the auction and the page down though, viewability can suffer. More immediately, so can impression numbers, page speed, usability and engagement which might not be as noticeable. As such it is important to understand the impact of adding each new bidder to your wrapper.
Work with the fastest bidders
It’s not just the number of bidders that can impact speed and viewability, but also your choice of bidders. Working with bidders who return their bids quickly lets you shave time off your timeouts and ensure that ads are served quickly.
Avoid or limit waterfalls and passbacks
The rise of Header Bidding, in particular, has greatly reduced the use of waterfalls in ad-serving, but they still serve a purpose for many. When the line item at the top of a waterfall fails to fill an impression and the passback is triggered this will introduce additional latency. Any latency will impact viewability, so this is something to be minimised.
Waterfalls now tend to be used when there are high-value deals to be had, so their use might be justified. When they are it is important to monitor their impact on viewability and carefully select what partners will be eligible to serve into the passback.
Use Asynchronous loading where possible
Asynchronously loading scripts helps avoid web pages being blocked from loading whilst the script runs. It’s not possible to run every script asynchronously, but using async wherever possible can ensure that content reaches the user more quickly and ads load fast.
Use the latest version of all scripts
Wherever possible use the latest version of all libraries and scripts so that you benefit from optimisations that the authors have made. If you use local versions of tags of libraries (such as prebid or GPT, or even non-ad serving scripts) ensure that they are regularly updated.
Improving ad viewability through content
This category of viewability optimisation is probably both the most difficult and the most important. In simple terms, more engaging content drives higher viewability. An example would be that a “more interesting” article is more likely to hold the user’s attention as they scroll through the page and view more ad placements.
An interesting example of this is seen when comparing Google’s own viewability data for Gaming content vs Law & Government.
Source: Google advertising platforms data, Global, September 2018
Whilst it would be impractical to suggest that publishers covering governmental content start including games to improve ad viewability, there are ways that publishers can alter their content strategy to support viewability. Ideas include:
- Use more video content as video ads generally score higher for viewability
- Invest in the best content that keeps readers engaged throughout
- Analyse scroll depth on content and consider using non-text content at key points to keep users engaged
- Understand the content types and topics that perform best for you and focus efforts there
Improving ad viewability through better ad serving
Select more viewable sizes
The size of an ad unit also has an impact on how viewable it is. Unsurprisingly, taller display units tend to score higher for ad viewability than shorter ones used in the same position, as they stay within the viewport for longer as the user scrolls. For video, larger players score best.
The most viewable size for a given position will depend on the content and layout it appears in. Whilst taller units have a tendency to be more viewable, shorter units have more likelihood to have 50% of their pixels in view if users are not scrolling. As ever, the lesson is to test and measure what works best for a given situation.
Lazy load ads
A very effective way of increasing viewability on below the fold content is to use lazy loading. Most ad servers (including Google Ad Manager) will, by default, load all the ads needed for a page as the page first loads.
Lazy load, by contrast, loads each ad just before it is needed as users scroll through the content. Because this results in ads only being requested if there is a very high chance of them being seen, this can have a very significant impact on viewability rates.
Lazy loading can also improve user experience by reducing the initial load of a page. Although the total load when lazy loading could actually be greater, that load doesn’t all happen as the page is first loaded. This can help the page feel faster and more responsive.
The downside of lazy loading is that, by default, the impression count will drop. Because impressions are not served until they are likely to be seen, there will be fewer total impressions. That can seem counter-productive, particularly as it will often cause a short term drop in revenue. Over a longer-term, however, the aim is to increase the overall value of your inventory which will usually give a net gain for publishers. However, there are some things that you should consider before you implement lazy loading if your aim is to improve viewability and increase revenue:
Viewability bucket rank
When bidding on ad inventory, advertisers are able to filter based on ad viewability ranking. This is usually organised in increments of 10%. This means that if you improve your ad viewability from 61% to 69%, your inventory would still be within the ‘60% or greater’ rank. It is best to try and aim to get into the next bucket rank if you want to see CPM gains. However, note that if your ad viewability is already 80% or above, then lazy loading is unlikely to have a significant impact on either viewability or CPM rates.
Device type
Implementing lazy loading for mobile users typically results in a greater increase in CPM rates, despite having less impact on viewability. For desktop users, the opposite is true. Desktop ad viewability and CPM rates are generally greater than mobile anyway, so if your viewability on desktop is already high, you are unlikely to see significant revenue improvements.
Target GEOs
Implementing lazy loading for users in target GEO markets has a greater CPM uplift than for users in non-targeted GEOs. This is because you will see better viewability with the GEOs that you are targeting because those users are more likely to engage with your content. Users in target GEOs will have better viewability scores because they are more likely to engage with your content. As such, you are likely to see a greater CPM uplift through implementing lazy loading for users in target GEO markets than for those users that are not in your target GEOs.
Use “sticky” ads and adhesion units
Some ad placements are designed to maximise ad viewability by staying within the viewable area of the screen for longer. Sticky ads appear in the main page, and “stick” in view as the user scrolls past them.
Adhesion ads are those that stick to either the top, bottom or side of the screen to stay in view.
Both approaches are effective in terms of boosting viewability, but have to be implemented with care to avoid having a negative impact on user experience. Care also needs to be taken with these types of units to stay within the ad serving policies of your ad vendors and to avoid accidental clicks and invalid activity.
Refreshing ads in view
If you use any sort of ad refreshing strategy, use a script that will only refresh ads that have been viewed and are currently in view. This not only gives the original impression the maximum opportunity to be viewed but also increases the likelihood of subsequent impressions being viewable.
OKO Smart Refresh : Rather than simply refreshing and ad 30 seconds after it loads, OKO Smart Refresh ensures that each impression has been in view for 30 seconds before it is replaced. The impression is then only replaced when in view to give the following impression every chance to be seen.
