This article explains, for Sizmek Ad Suite, how Sizmek counts Impressions, Ad Starts, Clicks, and Ad Requests to determine reasons for possible discrepancies.

Impression Counting

Impression counting is client-side. When an ad request arrives at the server, the server logs the request.

Sizmek Ad Suite counts impressions when a single asset finishes loading and starts rendering.

3rd Party impression tags are fired immediately after Sizmek sends the impression to be loaded.


Note: Since there is no code, tracking pixels impressions are counted as soon as the call reaches the server.

Ad Start

Ad Start occurs when the ad is loaded into the end-user environment, for example, into the browser or mobile app. Sizmek reports the Ad Start only if the ad is fully loaded and only when Verification and Viewability are enabled.

The system uses different methods for Image, HTML5, and Flash to detect the exact timing for loading the actual content:

  • Image: Sizmek triggers the Ad Start event when the image is fully loaded.

  • HTML5: Sizmek triggers the Ad Start event when the main iFrame is fully loaded.

  • Flash: If the browser permits, Sizmek reports Ad Start when the second frame is played; otherwise it reports Ad Start as soon as the flash is played.


Sizmek Ad Suite only counts the first click, for any single ad session, as a click; any additional clicks are considered interactions. Sizmek Ad Suite is IAB click certified and uses click data for analytics purposes.


Note: The first click is also counted as an interaction.

Ad Request


Note: Ad Request is only supported in Sizmek Ad Suite.

IAB defined a standard, for impressions, in which served impressions are counted only when the ad is loaded into the browser. This standard led to discrepancies between the serving platforms and the publishers impressions because the publishers count a higher number of impressions than the serving platforms.

To align these two counters, Sizmek has introduced a metric that counts the requested impressions (and not only the served impressions).

If this information is required for MDX2.0 (for publisher certification), it can be extracted by client services.

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