Publishers Guide to Ad Viewability Optimization

Ads viewability definition

Ad viewability measures the ad impressions actually seen by people, rather than just counting all measurable impressions of ads delivered by an ad server.

The fact that an ad was served doesn’t guarantee that it was seen. That’s why digital advertisers and publishers alike are increasingly measuring ad viewability rather than simply counting served impressions. Viewability determines whether an ad can actually be seen by viewers, according to a set of standards. For example, if an ad is displayed bottom of a web page and a visitor does not scroll down far enough to see it, it won’t be deemed viewable or included in viewable impressions calculations.

What is viewability threshold?


The Internet Advertising Bureau’s (IAB) and Media Rating Council’s (MRC) standard definition for ad viewability determines that at least 50% of the ad must be in view for at least one second on the web page for display ads and two seconds for ads that include video in order to be counted as a viewable impression. However, in order to drive higher bids for their inventory, publishers may set other types of viewability criteria that differ from industry standards.

How to measure ad viewability?

Measuring viewability is a challenge for digital advertisers and publishers alike. Google created a technology called Active View to measure if served impressions on its ad network are viewable, and for how long.

According to Active View, a display ad is considered viewable when:


  • At least 50% of the ad is visible for at least 1 second and the ad is less than 242,500 pixels (970 x 250).
  • At least 30% of the ad is visible for at least 1 second and the ad is 242,500 pixels (970 x 250) or greater.

A video ad is considered viewable when at least 50% of the ad is visible while the video is playing for at least 2 consecutive seconds.

What is ad viewability in video ads?

Most viewability benchmarks determine that at least 50% of a video ad must be in view on the web page for at least two seconds.

Two seconds is the standard for mobile and desktop video ads served in various ad campaigns to be considered a viewable ad. Anything less than two seconds for video ads is considered low viewability in most ad campaigns.

Why is viewability important?

Advertisers want their ads to be seen. They decide their ad spend according to how the ad is served.

Factors like ad placements, page position, page load, and other features can impact the average ad viewability and promote more viewable ads.

Ad viewability standards

There are many techniques publishers can implement with the goal of improving viewability for their ad inventory including loading speed, ad size, responsiveness, and good design.

1. Loading speed

The longer it takes for ads to load, the greater the chance that the viewer will navigate away from a web page before they see a viewable impression. That’s why faster loading is important when trying to improve ad viewability.

To improve loading speed, it’s important to optimize resource loading in served ads, and remove unnecessary files and tracking codes. Asynchronous loading using Google Publisher Tag (GPT) API and AdSense tags can also help. These tools load ads independently of other page content and the page position, reducing bottlenecks.

Lazy loading is another helpful tool. It decreases impressions served out of view by making sure content and ads are only rendered when they are in the user’s viewport.

Last but not least, it’s important to reduce the number of ad calls made from one server to another via passbacks. This improves loading speed and therefore viewability.

2. Ad size and layout

Short, vertical ads have the highest viewability rate, especially on mobile. Data shows that the ad sizes that perform the best are 120×240, 240×400, or 160×600. To improve viewability and increase ad revenue, publishers should create inventory suitable for those specifications.

3. Responsiveness in design

Ads must adapt to the browser and platform the viewer uses when the ad loads. To improve ad visibility, ad networks often include mobile ads. Publishers must ensure that their inventory is compatible with various ad formats to boost viewability rates and prevent non-viewable impressions.

4. Implement good design principles

Implementing good ad design principles like a clear visual hierarchy and the right balance of white space is important in order to improve viewability. Good design makes an ad easier to read and understand, and better integrates the ad with high-quality content.

What causes ads to not be viewable?

Below the fold

If an ad unit is ‘above the fold’, or on the top part of a user’s screen where it can be seen by users without scrolling, it is visible to most of the website visitors. But not every ad position is above the fold. Since users often visit web pages from smartphones and other mobile devices, the mobile page design may impact where the ad is served and whether a user scrolls to see it. In general, ads get higher viewability when they are right above the fold.


To improve viewability, some publishers may choose to implement their ad units as “sticky ads.” A sticky ad is a fixed ad unit that stays visible while the user scrolls up or down on the page.

Ad blockers

Ad blockers can also lead to low ad viewability. Ad blockers are browser plugins or filters that hide ads or prevent them from loading. Since many ad blockers only scan a page after it has loaded and then either hide or remove ads, they can make it difficult to calculate viewability. In many cases, an ad impression is recorded as part of the impressions served, despite the fact that users did not see the ad.

Ad fraud

Ad fraud can negatively impact user engagement. Some publishers who want to increase the value of their ad inventories turn to purchasing traffic from dodgy affiliate networks and third parties. Unfortunately, a lot of this is bot traffic.

Improve your Core Web Vitals score

Core Web Vitals are a group of metrics that have the biggest impact on UX according to Google and other experts. They include:

  • Largest contentful paint
  • Cumulative layout shift
  • First input delay

Although Core Web Vitals aren’t directly related to ads, they can impact your viewability score. Improving Core Web Vitals minimizes problems that reduce viewable impressions, for example, slow page speed and layout shift (abrupt shifts in the user’s position on the page during page load). And the benefits don’t stop with digital advertising campaigns—Google’s search algorithm also drives more traffic to websites with higher-than-average Core Web Vital scores, leading to more viewership overall.

What is an ad viewability rate?

An ad viewability rate tracks the total viewable ad impressions for both video and display ads in an advertising campaign.

What is a good viewability score?

Advertisers look for an ad viewability score that is above 70%- At minimum viewability should be at least 50%. After ensuring ads are viewable, ensure the ad content is safe for your brand and engaging for your audience.


Malvertising, the practice of sprinkling malicious code into legitimate-looking ads is growing more sophisticated. GeoEdge’s holistic ad quality solution has you covered.


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