Glossary
What is Viewability?
Also called: viewability rate
Viewability measures how many ad impressions could actually be seen: viewable impressions as a share of measurable impressions.
हिंदी में पढ़ेंViewability asks whether a person had a chance to see an ad, not just whether it loaded. The usual metric is the viewability rate: viewable impressions divided by measurable impressions. In Google Ad Manager this appears as Active View % viewable.
An impression counts as viewable when at least 50% of the ad’s pixels are on screen for one continuous second, or two continuous seconds for video. The rule comes from the MRC guidelines and is used by Google’s Active View. In apps, viewability is measured through the IAB Tech Lab’s Open Measurement SDK, which passes on-screen signals to verification vendors.
Layout drives viewability. Ads far down the page, slots that load long before the reader scrolls near them and slow pages all pull it down. Lazy loading, sticky units and well-placed slots can raise it. Check the rate per ad unit, because a site-wide average can hide one weak placement.
Example
An ad unit records 10,000 measurable impressions, of which 6,500 are viewable. Its viewability rate is 6,500 ÷ 10,000 = 65%.
Why it matters to publishers
Buyers measure viewability and tend to bid more for placements that are usually seen. A low rate on one ad unit often points to a layout problem you can fix.