This article summarizes how Sizmek measures impressions for ads it serves to mobile devices, and how this measurement methodology is consistent with IAB mobile measurement requirements.

Traditional (Desktop) Impression Measurement vs. Mobile Impression Measurement

Traditional impression measurement for display advertising is based on server-side counting of impressions - when an ad request arrives at the server, the server records an impression.

IAB Requirements for Mobile Impression Measurement

IAB has stipulated that mobile impressions be counted on the client’s side to accommodate for the reliability and latency limitations of mobile devices and networks. This means that an impression should not be recorded when an ad request has occurred; an impression is only recorded when successful ad delivery on the client side is in progress.

IAB Guidelines for Client-Side Mobile Impressions 3.1 Ad Impression Tracking

The following details are key components of client-side measurement:

  • A valid ad impression may only be counted when an ad counter receives and responds successfully to a request for a tracking asset from a client. This count happens after the initiation of retrieval of underlying page content. For client-side ad serving, the ad content itself could be treated as the tracking asset and the ad server itself could do the ad counting.

  • A successful response by the ad counter can include but is not limited to:

    • Delivery of a beacon, which may be defined as any piece of content designated as a tracking asset. Beacons are commonly in the form of a 1x1 pixel image, but this guideline does not apply any restrictions to the actual media-type or content-type employed by a beacon response.

    • Delivery of a 302 redirect or HTML/JavaScript (which doubles as a tracking asset) to any location.

    • Delivery of ad content

  • Measurement of any ad delivery may be accomplished by measuring the delivery of a tracking asset associated with the ad.


IAB’s full guideline for mobile impression measurement can be found here.

Sizmek Mobile Impression Measurement: Qualifying as a Mobile Impression

An impression will be considered as a mobile impression by Sizmek and be subject to the mobile impression measurement mechanism if it meets all the following conditions:

  • The impression must originate from a mobile device (tablet/smartphone); the Sizmek ad server identifies the source of every impression.

  • The impression is for an HTML5 ad.

  • The impression does not originate from a 4th party tag.

Sizmek Client-side Impression Measurement

For counting mobile impressions, Sizmek employs a client-side measurement mechanism, which follows the IAB guidelines and ensures impression reliability. The Sizmek platform follows these steps to record a mobile impression:

  1. An ad request arrives at the Sizmek server. For desktop sessions, an impression would be recorded at this stage. For mobile sessions, it is not recorded.

  2. The Sizmek server returns a script to the client. This script requests ad assets, starting with the main ad creative file, typically named index.html. index.html is downloaded to the client.

  3. The client’s browser runs index.html. The index.html file always loads a JavaScript file called EB.js, which contains the Sizmek client API script. This script serves as the IAB beacon, the delivery of which marks a successful mobile impression.

  4. The client runs the Sizmek API script (the beacon) and waits for its successful completion. Only when it has finished loading does the client send a notification to the server, which records the mobile impression. No mobile impression is recorded if one of these steps fail. Sizmek waits for the beacon (script) to run successfully before recording a mobile impression.

Additional Ad Request Metric

In some cases, such as on exchanges or non-accredited ad servers used by publishers, the counting method for a mobile impression is the same as for desktop, resulting in a discrepancy between impressions. To align overall numbers, Sizmek reporting uses ad request an metric to help match requests for ads sent to Sizmek in these instances.

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