The answer to this question is vCPM (Viewable cost-per-thousand impressions)
vCPM: vCPM stands for cost per thousand viewable impressions. Simply put, advertisers will pay according to the impressions that are viewed, not the creatives that rendered on the publisher’s site.
If CPM is cost per 1000 impressions, then vCPM would be cost per thousand viewable impressions. Viewable impressions are ad creatives that are actually seen by the users. But how would you determine which ads are seen? To simplify it, publishers have the MRC provided setups which define whether an ad would be considered as viewed or not:
For display ads, at least 50% of the ad (or ad pixels) should be visible on the user’s screen for more than 1 second.
For large ads, at least 30% of the ad (or ad pixels) should be visible on the user’s screen for more than 1 second.
And for in-stream video ads, at least 50% pixels should be visible on the user’s screen for more than 2 seconds.
Calculating the exact number of viewable ad impressions could be tricky. And even after you know that an ad is active on a user screen, there is no guarantee that the user has seen it. Hence to solve this, the standards defined by MRC offer some ideas about how viewability can be calculated.
