What is viewability?
Viewability measures whether an ad was actually on screen long enough to be seen. An ad can be served and counted as an impression while sitting below the fold, in a background tab or off screen. A viewable impression met a minimum standard for pixels in view and time on screen.
The standard most of the industry uses comes from the Media Rating Council (MRC) in the US.
How viewability is measured
A measurement script or SDK runs with the ad and checks its position on the screen. Under the MRC guidelines, an ad counts as viewable when:
Display: at least 50% of the ad's pixels are in view for at least 1 continuous second.
Large display: for ads of 242,500 pixels or more, such as a 970x250 billboard, the threshold is 30% of pixels for 1 continuous second.
Video: at least 50% of the player's pixels are in view for at least 2 continuous seconds.
Not every impression can be measured. Some environments block measurement scripts, so viewability is calculated only on measured impressions. Methods also differ by environment: in mobile apps, viewability is usually measured through an SDK rather than a browser script, so app and web results are not always directly comparable.
How to calculate viewability rate
Viewability rate = viewable impressions / measured impressions x 100
For example, if 80,000 impressions were measured and 56,000 met the standard, the viewability rate is 56,000 / 80,000 x 100 = 70%.
Some buys are priced on viewable impressions only, using vCPM. That shifts the risk of unseen ads from the buyer to the seller.
Why viewability matters
An ad that was never on screen cannot do its job, yet it can still cost money under a standard CPM buy. Tracking viewability helps you:
Avoid paying for placements that are rarely seen, such as slots far down long pages.
Spot suspicious inventory, since very low viewability can be a sign of ad fraud like ad stacking or hidden ads.
Compare the real cost of reach across sites, apps and deals.
Common ways to improve it: favor placements near content, use formats that stay in view, exclude low-performing sites and apps, and set viewability targets in your DSP where available.
Viewability vs attention metrics
Viewability is a minimum bar: the ad either met the threshold or did not. Attention metrics go further and estimate how much attention an ad actually got, using signals like time in view, scroll speed, interaction and models trained on eye-tracking data. Viewability tells you an ad could be seen. Attention tries to tell you whether it was. For video, pair viewability with video completion rate for a fuller picture.
Viewability with AdGeeks
DV360 measures viewability with Google's Active View, and Amazon DSP and Adform also report on it. AdGeeks traders monitor viewability by placement, cut inventory that is rarely seen and balance it against cost and outcomes. To see how much of your spend is actually viewable, request access.
