By all accounts, digital advertising should be easier to measure than traditional forms of advertising, like TV or magazine ads. As technology becomes increasingly sophisticated, we’re able to draw on more user data and serve ads in more elegant, reliable ways—yet until recently, there’s still been a major hurdle to measuring video ad effectiveness accurately.

What Are Viewable Impressions?

“Viewable impressions” serve as a distinction from the previous metric used to measure video ad effectiveness: “served impressions.” Served impressions are direct measures of how many times an advertisement was transmitted to a receiving user device. Similar but distinct, viewable impressions are measures of how many times an ad was capable of being seen by a user. For example, there are cases where an ad would count as a served impression, but not as a viewable impression, such as when a page fails to load, or when the content of an ad is not rendered properly.

This is an important distinction because much is predicated on the visibility of an ad. If you assume even 5 percent of all “served” ads are not considered “viewable,” this could result in heavily skewed data on ad performance, and worse, wasted money for the advertiser. In short, viewable impressions are a much more accurate and comprehensive measure, and accuracy is critical to maintaining a positive bottom line.

How Are Viewable Impressions Measured?

There are a few different standards of viewability. The main one to focus on is based on a set of simple parameters; to be counted as “viewable,” a display ad must have 50 percent of its pixels (or more) visible for at least one continuous second within the frame of a browser. For video ads, 50 percent of the pixels must be visible for at least two continuous seconds within the frame of a browser. This may not seem like a major threshold, but it can result in much more accurate ad viewing data.

What Affects Viewable Impressions

There are several independent factors that can affect whether an ad is considered viewable. Currently, the average viewability of an ad on an online source other than YouTube is a measly 54 percent on desktop devices. On YouTube, that rate is 91 percent.

Mobile devices, however, offer significantly higher visibility. The jump for YouTube isn’t much—growth from 91 to 94 percent—but desktop device video ad visibility leaps from 54 percent to 83 percent on mobile devices. Considering the majority of all web traffic now comes from mobile devices, this is good news for video advertisers.

Other factors that can influence viewable impressions include:

Optimizing for these factors will help you attain a higher viewability rate—though if you’re tracking viewability accurately, you may not have to pay for any served impressions that weren’t visible, mitigating your losses.

IAB’s Transaction Principles

IAB, a major video ad authority, has come up with a list of “transaction principles” related to ad visibility, which all advertisers and publishers should adhere to:

The goal is, obviously, 100 percent viewability, but this is not technically or commercially feasible right now. The IAB will put forth new transaction principles as it becomes more realistic.

The Bottom Line for Your Business

This article has offered a ton of information about viewable impressions and why they matter, but what practical takeaways can we surmise from this information?

First, stop thinking about your ads in terms of served impressions. You owe it to your campaign and your brand to seek viewable ad impressions—both in an effort to maximize the potential reach of your advertising, and to gather more accurate insights about your ad performance. Second, work with a vendor with a reliable system for measuring these metrics—you don’t want to be left with questionable data. Finally, learn more about the state of video ad viewability, and stay abreast of new developments as they roll out. Technology is always moving forward, and it pays to be on the cutting edge.