vCPM

What counts as viewable

The standard most buyers mean is the Media Rating Council's. A display ad counts as viewable when at least 50% of its pixels are on screen, in a browser tab that is in focus, for at least one continuous second. Large display ads of 242,500 pixels or more, such as a 970x250 billboard, count at 30% of their pixels. A video ad needs 50% of its pixels on screen while two continuous seconds play.

vCPM prices only those impressions. An ad that was served but never met the bar is not billed at all.

Converting between CPM and vCPM

The link between the two is the viewability rate: the share of served impressions that turned out to be viewable.

That is why the same slot can look expensive on one rate card and cheap on another. Before comparing prices, find out which kind of impression each one counts.

Why buyers prefer it, and what it means for you

A buyer paying on viewable impressions stops paying for ads below the fold on pages nobody scrolled. Google Ads offers viewable CPM bidding on its Display Network for the same reason. For a publisher it cuts both ways: fewer impressions are billable, each billable one is worth more, and the placements people actually see become easy to price above the ones they do not.

• Move or remove slots that are rarely seen. They drag down your averages and your credibility.
• Price slots near the top of the page and inside the article above footers and low sidebars.
• Say which viewability standard you bill on, so nobody has to guess.

How Pyrobid measures it

Pyrobid bills only impressions that were seen. The ad's position is checked every 100 milliseconds in the reader's browser, and an impression becomes billable once at least 50% of the ad (30% for ads 500 pixels wide or more) has stayed on screen for more than 300 unbroken milliseconds. That matches the MRC's 50% for ads under 500 pixels wide, such as a 300x250, asks less of some wider ones, such as a 728x90, and uses a shorter dwell time, so overall it is a more forgiving bar than the MRC benchmark. If you sell to a buyer who audits against the MRC standard, quote them these numbers as they are. The viewable impressions page has the detail.