Glossary
What is Viewable impression?
Also called: viewable ad impression
A viewable impression is an ad with at least 50% of its pixels on screen for 1 continuous second, or 2 seconds for video.
हिंदी में पढ़ेंA viewable impression is an impression that had a real chance to be seen. The rule comes from the MRC (Media Rating Council) Viewable Ad Impression Measurement Guidelines: for display, at least 50% of the ad’s pixels must be in view for at least one continuous second; for video, 50% for two continuous seconds.
Google Ad Manager’s Active View measures against the same standard. Not every impression can be measured, so the viewability rate is viewable impressions divided by measurable impressions, not by all impressions. In apps, the IAB Tech Lab’s Open Measurement SDK reports how much of an ad is on screen and for how long.
The MRC also allows a lower 30% pixel threshold for very large display ads, if it is disclosed. Ads far down a page that nobody scrolls to, or ads that load after the reader has left, can count as impressions but not as viewable ones.
Example
An ad unit serves 900 impressions, all measurable. 600 of them meet the 50% / 1 second rule. Its viewability rate is 600 ÷ 900, about 67%.
Why it matters to publishers
Buyers measure viewability and tend to bid more for placements that are usually seen, so viewable impressions shape the CPMs a site earns.