Viewability is an online advertising metric that aims to track only impressions that can actually be seen by users. For example, if an ad is loaded at the bottom of a webpage but a user doesn’t scroll down far enough to see it, that impression would not be deemed viewable.

Viewable Display Ad Impressions are counted when the following criteria are met:

• 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.

Optimal viewability percentage in digital advertising industry is 55-65%. Anything below these numbers is considered as low viewability inventory with lower performance.

Example of viewable and not viewable impression: