Viewability, what the rate means and how to improve it

Viewability is the share of your served impressions that were actually on screen. It answers a question the impression count can't: the ad rendered, but was it in front of anyone?

How we measure it

We record a viewed event when at least 50% of the ad's pixels are on screen for at least one continuous second, the IAB standard, measured in the browser by the tag. The event is only accepted after the ad has rendered, and it is deduplicated per impression, so the viewed count can never exceed the served count.

The rate is:

viewability = viewed ÷ served impressions

The denominator is served impressions, the render-confirmed event we bill on, never ad requests. Every served impression in the window counts toward the rate, including impressions that were filtered and never earned: the population is all of your traffic, not a subset. See What is a served impression for the difference between a request, a render, and a view.

Measured, not billed

Viewability is reported so you can see it. It does not change what anyone pays, billing is on served impressions, unchanged. A low rate costs nothing directly, but it is a signal about where the ad sits on the page, and it's yours to act on.

Reading the number

• Shown to one decimal, over the trailing 30 days, on your dashboard tile and per zone in your zone list.
• A zone with no served impressions in the window shows —, not 0.0%, because there is nothing to measure yet, and we won't claim a rate we don't have.
• We never hide a low-volume rate behind a threshold. A zone with 20 impressions shows its exact rate, and the impressions column beside it tells you how much weight the number deserves.

How to improve it

The rate is mostly a placement question, and placement is something you control. What moves it:

• Put the zone where people actually look. A slot in the first screenful is seen far more often than one several scrolls down an article.
• Don't stack zones. Several slots in a vertical run means the lower ones rarely reach 50% on screen before the reader turns away.
• Keep the container visible. A zone inside a collapsed accordion, an inactive tab panel, an off-screen carousel slide, or a container with no height will render and never be seen.
• Reserve the slot's height in your layout. If content above the ad loads late and shoves the slot past the viewport, the ad rendered but nobody was there for it.
• Expect some gap, always. An ad painted in a background tab, or one a reader scrolls past in under a second, is served and not viewed. That is ordinary reading behavior, and no placement is ever 100%.

What this number is not

Viewability measures where the ad sat on the page, not who was on the page. A perfectly good audience reading a page with the ad slot far down will produce a low rate, and that is a layout finding, not a traffic finding. The traffic side is reported separately, on its own terms. Publishers see it under Filtered traffic on your zones, and the full counting rules live in How we count & filter traffic.