Ad Viewability
The percentage of ad impressions that are actually visible to users on their screens.
What is Ad Viewability?
Ad viewability measures whether an ad was actually seen by a user, not just served by the ad server. The Interactive Advertising Bureau (IAB) and Media Rating Council (MRC) define a viewable display ad impression as one where at least 50% of the ad's pixels are in the viewable area of the browser window for a minimum of one continuous second. For video ads, the threshold is 50% of pixels visible for at least two continuous seconds.
Viewability has become a critical metric because advertisers realized they were paying for impressions that users never saw — ads below the fold that were never scrolled to, ads in background tabs, or ads that loaded after the user navigated away.
Why It Matters for Publishers
Viewability directly affects your CPMs and revenue. Advertisers are willing to pay significantly more for highly viewable inventory. A site with 80%+ viewability can command CPMs 2-3x higher than a similar site with 40% viewability. Many premium advertisers now require minimum viewability thresholds (often 60-70%) before they will bid on your inventory.
Google Ad Manager and most SSPs provide viewability scores at the ad-unit level. If certain ad units consistently score below 50% viewability, they are dragging down your overall site quality score and may even prevent premium demand from bidding on any of your inventory.
Tips for Optimization
- Prioritize above-the-fold placements: Ads visible without scrolling have the highest viewability rates. A leaderboard at the top of the page typically achieves 60-80% viewability.
- Use sticky ads: Sidebar sticky units and anchor ads that follow the user's scroll maintain near-100% viewability as long as the user is on the page.
- Implement lazy loading: Load ads only when they're about to enter the viewport. This prevents impressions from being wasted on ads that would have gone unseen.
- Reduce ad clutter: Pages with fewer, well-placed ads typically have higher viewability than pages stuffed with dozens of ad units. Quality over quantity applies here.
- Monitor and remove low-viewability units: If an ad unit consistently scores below 30% viewability, it's hurting your overall metrics. Remove it or relocate it to a better position.
Further Reading
Learn how to optimize viewability across your entire site in our guide to viewability optimization, or see how ad placement affects viewability in our ad placement best practices guide.