A viewable impression occurs when at least 50% of an advertisement's pixels are visible on a user's screen for a minimum of one continuous second for display ads, or two continuous seconds for video ads. This standard, established by the Interactive Advertising Bureau (IAB) and Media Rating Council (MRC), ensures that ads have a reasonable opportunity to be noticed by users.
The concept of viewable impression emerged from the recognition that traditional impression counting was flawed. Previously, an impression was counted whenever an ad was served to a webpage, called Served Impressions, regardless of whether users could actually see it. This meant advertisers were paying for ads that loaded below the fold, in hidden tabs, or were otherwise invisible to users.
Served Impressions vs. Viewable Impressions
Digital marketing teams track impressions to measure the total digital footprint of their advertisements. In this effort, it is important to distinguish between served impressions and viewable impressions.
Served Impressions include all delivered ads, even those that might be hidden from users.
Viewable Impressions include delivered ads where at least 50% of the ad's pixels are visible on screen for a minimum of one second (two seconds for video ads).
The gap between served and viewable impressions can be large and a substantial portion of served impressions may never reach their intended audience. As an example, Pixelate's 2025 Q1 report shows 58% viewability rate for desktop web ads globally, which implies that 42% of served impressions were never seen by a human.
Technical Measurement Standards
Display Advertising Standards
For standard display advertisements, the viewability threshold requires:
- At least 50% of the ad's pixels must be visible within the viewable area of the browser
- The ad must remain visible for at least one continuous second
- Measurement occurs through JavaScript-based tracking or other approved methodologies
Video Advertising Standards
Video advertisements have slightly different requirements:
- At least 50% of the video player's pixels must be visible
- The video must be playing (not paused) for at least two continuous seconds
- Audio is not required for viewability measurement
How Served Impressions Affect Your Marketing ROI
For optimizing marketing ROI, it is interesting to measure your spend on ads that are seen by buyers, and whether those impressions are helping you to drive more incremental sales. For understanding the incremental sales impact of ad campaign you should use a method that estimates the true incremental sales lift, such as Marketing Mix Modeling (MMM).
Conclusion
When measuring the number of impressions, it's important to understand whether you are measuring served impressions or viewable impressions. Only impressions that are seen by buyers have a chance of driving them to your eCommerce store to purchase your products or services.
Authors
Lauri Potka is the Chief Operating Officer at Sellforte, with over 15 years of experience in Marketing Mix Modeling, marketing measurement, and media spend optimization. Before joining Sellforte, he worked as a management consultant at the Boston Consulting Group, advising some of the world’s largest advertisers on data-driven marketing optimization. Follow Lauri in LinkedIn, where he is one of the leading voices in MMM and marketing measurement.