• by Laurie Sullivan  @lauriesullivan, May 8, 2015

The average viewability of video ads across the Web -- not including YouTube -- is 54%, and on YouTube it is 91%.

It's no surprise that video ads are significantly more viewable on mobile and tablet than on desktop, but it highlights the shocking fact that 46% of video ads across the Web are never seen, and 76% of non-viewable ads never had a chance to be seen. 

The study, released Friday, suggests that those video ads not seen run in the background, hidden by another Web page, meaning that the front tab hides the page with the image running behind it. The remaining 24% were scrolled off-screen or abandoned in fewer than two seconds.

Google has long been an advocate of the ability to measure when and where ads appear, and the length of time viewers remain with the ad or content. They measure viewability on everything from search to display, and now video.

The study benchmarks the number of video advertisements seen across the Web and on YouTube by analyzing two sets of data in April 2015. The first looks at video viewability across desktop, mobile and tablet, not including YouTube. The second analyzes video viewability data for YouTube, including both data from across the Web, such as desktop, mobile, and tablet, and mobile in-app ads.

A viewable video impression occurs when at least 50% of an ad's pixels are visible on screen for at least two consecutive seconds, according to the Media Rating Council and Internet Advertising Bureau (IAB) standard.

Player size and position determine viewability. Video ads are significantly more viewable on smartphones and tablets, compared with the desktop. Video is 83% viewable on mobile devices, 81% viewable on tablets, and 53% viewable on desktops. More than half of YouTube views are on mobile devices. YouTube is 94% viewable on mobile devices, smartphone and tablet, and 87% more viewable on desktop.