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What Advertisers Should Know About Impressions vs. Viewable Impressions

A common mistake in the digital marketing industry is to think the number of impressions an ad has equals the number of times an ad has been viewed. How could it not be? This is one of the metrics you are almost guaranteed to see when you first enter a platform, and is often used to calculate other important performance indicators such as click through rate, cost per mille, and more.

An impression is NOT how many people viewed the ad, but rather the number of times users had the chance to view it somewhere on a webpage. An impression might be counted if a user goes to a loaded page and leaves half a second later. An impression might be counted if a user stays on a page for five minutes but never scrolls below the fold to find your ad at the bottom of the webpage. Yet, many are still using this metric of an impression to base major marketing decisions off without checking the validity of them.

This is because many marketers confuse the definition of an “impression” with the definition of a “viewable impression”. Even marketers that are aware of this distinction may not know a lot of the details on how viewable impressions are determined and what they can do to improve their own ads’ viewability.

The definitions of an impression might vary across platforms, such as:

Facebook Viewed Impressions

“We measure an ad impression the moment an ad enters the screen of a desktop browser or mobile app. If an ad doesn’t enter the screen, we don’t count it as an ad impression.” - Facebook Business


“Each time your ad appears on Google or the Google Network, it's counted as one impression.” - Google Support

“A link URL records an impression when it appears in a search result for a user. Whether or not the link must actually be scrolled into view or otherwise visible depends on the type of search element that contains the link, as described later.” - Google Support

Often, an impression is registered when the ad is served to a page, even when a platform is fully aware the user did not see the ad.

Viewable Impressions

The Media Rating Council (MRC) in collaboration with the Interactive Advertising Bureau (IAB) have produced a standard for what is considered a “viewable impression”. This impression must fit two criteria:

  • Pixel Requirement: Greater than or equal to 50% of the pixels in the advertisement were on an in-focus browser tab on the viewable space of the browser page, and
  • Time Requirement: The time the pixel requirement is met was greater than or equal to one continuous second, post ad render.

From a sample of Merkle advertiser data in Q4 of 2018, only 54% of display impressions are considered viewable impressions by the MRC and IAB’s definition.

Fortunately, there are options to measure if your impressions are viewable. Many platforms, including Google Ads, contain “viewable impressions” as a data pull column so that you can easily access this information. Vendors such as IAS, Moat, and DoubleVerify help can be utilized to help ensure viewability and valid traffic. These vendors track ads to verify they are being viewed at a stronger precision than what you might find on a normal platform such as DV360. These vendors are considered an extra safety step and only recommended for brands with a higher than average concern for viewability and brand safety.

Why still care about impressions?

Impressions, even when not viewable, are still an essential metric. This lets advertisers know how many times they have beat the competition in an auction for the chance to have a consumer to view their ad. All of the work of the digital marketer, platform, and exchange lead up to whether or not the ad receives an impression. What is important is to remember that these ads were only served and not necessarily viewed, and that you should look at both impressions and viewable impressions to gain a complete picture of any digital marketing campaign.

Using Impression Data

Using both impressions and viewable impressions gives you a plethora of information on who is seeing your ads. This allows you to optimize your campaigns in a variety of ways, including:

  • Prioritizing platforms and exchanges where your ads are being seen
  • Optimizing your campaign with platform-specific tools, such as viewability minimums, made to increase the likelihood of your ads landing above the fold
  • Testing different ad sizes to see which have a higher percent of viewable impressions. One advertiser saw an 11% higher rate of viewable impressions to impressions on a 320x50 ad compared to a 728x90 ad.
  • Using vendors such as IAS, Moat, and DoubleVerify to ensure a certain level of viewability.

It is important to keep in mind that with any optimization there is risk involved. When prioritizing inventory where you are more likely to be seen, CPMs typically increase, sometimes dramatically. As always, digital marketing is both a science and an art, so it will take multiple rounds of testing to find the best fit for any campaign.  Now that you’re armed with the knowledge of metrics to use, go test!