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  • In 2007, Alenty was the first company to successfully measure ad-viewability. Alenty was later acquired by AppNexus in 2014.
  • In 2012, the Interactive Advertising Bureau (IAB) defined a "viewable impression."
  • In 2014, the Media Rating Council (MRC) lifted its ban on trading viewable impressions.

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IAB Viewability definition: 50% of the pixels of a regular creative or 30% of the pixels of a large size creative (242,500 pixels or greater), are on an in-focus browser tab, on the viewable space of the browser page, for a minimum of one continuous second.


The following are examples of creatives that are not viewable:

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Viewability depends on a myriad of parameters: screen size, creative loading duration, etc.  


Viewability measurement is achieved by javascript embedded within the creative. This script is called for each individual ad-impression. It launches automatically as the page loads and immediately starts measuring if and when the creative is viewable.

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The primary method that the script will use to determine whether an ad is viewable is "page geometry", which takes into account the size of the screen and the size and position of the creative on the page among other factors such as scrolling and window focus. However, if only a part of the required information is available, other techniques must be used so that the measurement is consistent across all platforms.


Viewability measurement must work in all environments and provide consistent results. IFrames are the most challenging of technical environments. When the creative and the measurement script are served within an IFrame, regular geometric methods cannot be applied. Alternative methods, such as browser optimization, must be developed. Depending on the technologies used by ad-viewability vendors, the potential success rate can be very limited.

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Using Viewability Data