Optimize your bidding with viewability data

You can use Active View viewability data from Ad Exchange to understand the probability that an impression will be seen by a user. Viewability enables you to make smarter bidding decisions and provides insight and transparency into the potential value of publisher inventory to optimize your bidding on Ad Exchange. When ads are rendered by a third-party SDK, all ad impressions will be shown as "Not viewable" because the impressions are not measured by Active View.

More information about how viewability works

Scenario 1: Consider a placement at the bottom of a webpage, where the user needs to scroll down to see the bottom of the page. This user might not see the ad before navigating away.

Scenario 2: Consider the same placement, however, the user has a larger screen. The entire page, including the ad, appears in the viewable space.

Both scenarios count as impressions, but only viewability provides data to understand whether the ad is likely to be visible to the user.


An impression is considered viewable when it has the opportunity to be seen in the user's browser. The Interactive Advertising Bureau (IAB) defines a viewable impression as an ad that meets the following criteria:

  • For display inventory: 50% or more of the creative on screen for a continuous 1 second or more
  • For in-stream inventory: 50% or more of the creative on screen for a continuous 2 seconds or more

Obtain viewability data from the bid request

When viewability data is available for the impression, Ad Exchange will pass the viewability rate to RTB buyers in a field in the bid request.

In the BidRequest RTB buyers receive, the optional int32 viewability field will contain a value, either expressed as a percentage between 0 and 100, or -1.

The value of -1 indicates that historical viewability data is not available. This could be because the inventory is currently out of scope for Active View, or because the publisher's implementation creates measurement challenges.

Learn more in the proto definition.

Viewability versus above-the-fold targeting

We recommend that buyers use the viewability signal, when available, rather than the above-the-fold (ATF) or below-the-fold (BTF) signal. ATF impressions may or may not meet the IAB standards for viewability.

In several studies, we have found that viewable impressions are a better predictor of user engagement and client performance than ATF and BTF heuristics. If a buyer updates their bidding logic to only bid on inventory that is both ATF and above a certain viewability rate, they will very likely decrease the number of impressions they bid against.

If you are pretargeting ATF, you are only eligible to receive bid requests for above-the-fold inventory. We suggest that you modify your pretargeting configuration to remove the above-the-fold targeting, so that you are eligible to receive bid requests for both ATF and BTF inventory and use the Active View information to assess the value of the inventory.

Frequently asked questions

What is the difference between Active View and viewable impressions?

Active View is the name of Google’s proprietary technology for enabling viewable impressions tracking and measurement of display and video ads. “Viewability” is a broad term referring to the percent of viewable impressions compared to measurable impressions.

Viewable impressions are defined per the IAB standard metric:

  • For display inventory: 50% or more of the creative on screen for a continuous 1 second or more
  • For in-stream inventory: 50% or more of the creative on screen for a continuous 2 seconds or more
For what inventory can I expect to see viewability information?

Viewability data is currently available for display and video inventory, across desktop, mobile web, and mobile app.

Is viewability data available for third-party Ad Exchange inventory only or also for AdSense?

Viewability data is available for measurable impressions across both AdSense and Ad Exchange inventory.

Are there cases where viewability data is unavailable for display inventory on the web?

Yes. Some site and tagging configurations, like cross-domain iframes, are harder to assess viewability data. However, we expect that to grow as we work with publishers to improve the measurability of their inventory.

Why would Google not be able to measure the viewability of all impressions?

The most common reason for non-measurement is the placement of the publisher ad tag within a cross-domain iframe. The use of legacy tags, custom JS or XML ads are not supported by Active View.

Can a publisher opt out of having their inventory measured for viewability?

No. A publisher cannot opt out of having their inventory measured for viewability. All publishers are opted in for viewability, by default. Ad Exchange provides reporting to publishers so they can verify how much of their inventory is measurable and how much of their measurable inventory is viewable.

How is viewability data determined?

Viewability data is the percentage of measurable impressions in an ad block, that were viewable. The percent is based on data for the previous 7 days, and is updated daily.

The viewability rate is associated with an ad block, which is a set of similar ad slots across a publisher’s inventory.

Is the viewability rate in the bid request for the exact ad slot associated with the request?

No. The viewability rate is associated with an ad block, which is a set of similar ad slots across a publisher’s inventory.

Can a buyer pre-target based on viewability?

No. Buyers cannot pre-target based on viewability. Buyers can only use the viewability information passed in the bid request as an additional signal to further optimize bidding decisions.

Will above-the-fold information continue to be passed in the bid request?

Although we recommend using viewability signals over the use of ATF and BTF targeting, we will continue to pass ATF and BTF information in the bid request when it is available.

Is post-impression Active View information available in reporting?

Post-impression Active View information is not currently available in reporting, but we are hoping to make it available in the future.

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