Definition: Viewable Impression [VI]

What is a Viewable Impression?

A Viewable Impression (or VI) means an ad impression that appears on-screen.

These impressions are called viewable, as although we cannot know where every user is looking on a screen, an ad appearing on-screen means there was at least the opportunity for it to be seen. This is as opposed to an ad that was loaded onto a page below the fold (and never seen by anyone).

The reason this type of ad impression came about is that previously (as late as 2014) 54% of all ads were loaded in places they would never be seen by anyone. This is actually due to a relatively small percentage of websites delivering a very large amount of these ads.

It was enough of a problem that the advertising industry has worked to address it, however.



Viewable Impression Definition

A viewable impression is defined by the IAB as being at least 50% on-screen for at least one continuous second. It also has to be on an “in-focus” tab – meaning the tab in the browser is actually being used.

For expandable ads, this definition only applies to the pre-expanded ad.

For videos, a viewable impression means 50% of the video has to have been on-screen for at least two consecutive seconds.

A viewable impression is considered as an “Opportunity To See” which is a traditional marketing metric used to measure how many times a user comes in contact with a message. It is generally thought that five “opportunities to see” is optimal.


What it looks like

What It Looks Like: Viewable Ad ImpressionsClick to enlarge


Technical Information

Different companies use different methods to measure whether ads are actually viewable. For example, Google uses its own program called Active View in all its products.

The overall standards have been set out in the IAB has set out its guidelines here. It’s, of course, quite a dry read, but if you are in doubt you can skim it and get the gist quite quickly.

The main thing to note is screen size. A website may be set out so that its ads are naturally above the fold (and therefore viewable) on a desktop screen. However, because of the huge variety in screen sizes, it is very likely that ads will not always appear in the same place relative to the fold.


Top Tip

Vertical ad units (such as a 160×600) have the highest viewability rate as they stay on-screen for longer. They still have a lower average CTR than 300x250s and 728x90s however, and so should be used in conjunction with (as opposed to instead of) other ad sizes.


Viewable Impression Advice For Site Owners

The easiest way to encourage your ads to be viewable is, of course, to place them above the fold. According to research by Google, however – the optimum place is in fact just above the fold, not at the very top of the screen.

It would be impractical to place all of your ads just above the fold, however. Therefore placing ads high up on your pages wherever they fit (while still respecting your design) is the best course of action. The Online Advertising Guide has tried to demonstrate best practise with our own ad placement.


Viewable Impression Advice For Ad Buyers

Viewable Impressions do generally perform better than other ad impressions. However, a CPVM campaign is only really an improvement on a CPM campaign. If your goal is tangible results (such as clicks on conversions), then you should still buy advertising on the appropriate basis (eg CPC or CPA).


Other names for Viewable Impressions (synonyms)

Viewed Impressions


It’s the opposite of (antonyms)

Non-Human Traffic (kinda)


Not to be confused with




Viewable Impression Definition



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