Viewability
Viewability is the degree or likelihood that an ad position is visible to a website visitor. The KPI ad viewability is expressed as a percentage of the total number of views in which a banner or banner position was actually in view.
Banners may not be "viewable" because they are covered by other parts of a page or because they are outside the browser's viewport and a visitor must scroll to see the position.
Steering for high viewability avoids buying ads that are not seen by visitors. This is especially important for CPM-based campaigns. Invisible ads placed on a CPC or CPA basis will not cost the advertiser anything, but will also fail to generate traffic, awareness and other value. Low viewability can also be an indication of ad fraud.
How is viewability calculated?
Since 2014, viewability and how it is calculated has been a standard set by the IAB. A banner is considered viewable once at least 50% of the pixels have appeared on screen for at least one second. For a video ad, this is at least two seconds. In practice, other, often higher criteria are also used.
