Viewable Impression

A viewable impression is an ad impression in which at least 50% of the ad's area is visible on screen and remains visible for more than one second. This standard was established by the International Advertising Bureau (IAB) to give advertisers a meaningful signal of whether an ad had a genuine opportunity to be seen — as opposed to being technically served but never actually in view.

The distinction matters because not every served impression reaches a real human eye. Viewable impressions help advertisers separate legitimate human exposure from impressions lost to bots, poor page placement, or user behaviour that prevents the ad from being seen.

An impression can be served without being viewable for several reasons:

• The user leaves the page before the ad view can be counted.
• The user sees less than 50% of the ad (e.g., it loads below the fold and is never scrolled to).
• The user has ad-blockers enabled.
• The page visit originates from a bot rather than a real user.
• The user's browser does not serve ads.
• The user opens the page on a device that does not enable ads.