AD-Vantage Glossary: Defining “viewability”

Also referred to as: Opportunity to see, viewable impression

Also referred to as: Opportunity to see, viewable impression

What it means

Viewability is a measure of how often an ad has the opportunity to be seen by a human user.


A display ad impression is considered viewable if at least 50% of its total area is visible in a user’s browser window, and remains there for at least one second. A video ad impression is considered viewable if it is 50% on-screen and plays for 2 consecutive seconds. The “viewability score” for a specific ad placement, site or campaign reflects the percentage of total ad impressions sent to the placement, site or campaign that fit the viewable criteria.

For example, a “viewability score” for a below-the-fold web banner of 50% means that half of the times users visited the page where that banner was hosted, it didn’t show up on their screen — either because it was too far down the page, it was hidden behind another object, it didn’t load properly, or the “user” wasn’t a real user at all.

Ad verification providers measure viewability by following each ad impression to the browser where it’s displayed using a line of code written into the ad called a tag. The tag sends back information about where the ad is in the browser window, whether it’s in an active browser tab, and whether it’s being drawn behind another object. This data can either be used to update the media’s viewability score in real-time, or it can be sent to a third-party measurement company, like Nielsen or comScore, which collect and verify the data and send a full report 1-3 days later.

What it means to you

No advertiser wants to pay for ads that aren’t being seen. So it’s no surprise advertisers don’t want to buy digital ads that end up in a bad location (like a billboard facing a wall) or don’t get delivered at all (like a newspaper that throws half its papers in the trash).

Viewability was developed as a way for advertisers to measure what fraction of their spend was at least making it to the consumer’s doorstep. Viewability scores offer a benchmark to help media planners compare placements and be confident that they’re getting the right value for their dollars. The data from viewability measurement can even be used to inform real-time decisions made by programmatic buying algorithms about which media to purchase (and which to avoid), to improve overall campaign performance.

It’s important to note that viewability is not a measurement of how often an ad was actually seen; 100% viewability does not mean that every ad you bought was seen by a consumer. An ad may be 51% on-screen, or on-screen for only 1.5 seconds, and it will be considered viewable even though it’s unlikely that the user took much away from it in those circumstances. And just like in other media, getting an ad in front of the consumer doesn’t mean they’ll pay attention to it — internet users can mute or ignore video ads on the Internet just the same as they do on TV.

So while viewability is useful for getting the best media, it can’t be used to arrive at a reliable estimate of audience size. For that, digital is no different than TV — the only way to determine whether your audience watched an ad is to ask them (with a representative panel study).

Where you can see it in the market

Viewability solutions are offered by a large number of third-party measurement and ad verification providers, such as comScore, Nielsen, Moat and Integral Ad Science. Many of these solutions are directly integrated into demand-side platforms, as a standard feature for clients. In some cases, demand-side platforms offer proprietary real-time viewability solutions. Notably, video DSP TubeMogul provides free viewability audits for pre-roll video campaigns.

The ad industry association responsible for defining and implementing viewability standards is Making Measurement Make Sense (3MS), a joint project of the Interactive Advertising Bureau, the Association of National Advertisers, the Media Rating Council and the American Association of Advertising Agencies. In video, the standard is supported by Open VideoView (OpenVV), a coalition of providers that hosts an open-source solution for publishers and video players to implement viewability measurement.

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