Definition
Viewability is the measure of whether a served ad actually had the chance to be seen by a human — typically defined, for display, as at least 50% of the ad's pixels in view for at least one continuous second (two seconds for video), with stricter custom standards also used. An ad can be served and counted as an impression while never scrolling into view, loading in a background tab, or sitting below a broken lazy-load, so viewability separates "delivered" from "viewable".
Viewability is a baseline quality filter for display and video buying. A low viewable rate means budget is paying for impressions no one could see; a high viewable rate is necessary but not sufficient for effectiveness (a viewable ad still may not be noticed or effective).
Buyers set viewability thresholds, pay on viewable impressions where possible, and use it alongside fraud, brand-safety and attention metrics.
In context
For iGaming media buyers running display and video (in compliant markets), viewability is part of routine campaign hygiene: setting a minimum viewable-rate threshold, excluding placements and sites that consistently fall below it, and where the deal allows, paying on viewable impressions rather than served ones. Poor viewability often travels with other quality problems — cluttered pages, ad stacking, made-for-advertising sites — so it is a useful screen for weeding out low-value inventory before looking at conversion data.
Viewability also interacts with the conversion measurement affiliates care about. For a performance buyer, the downstream metric (cost per FTD, ROI) ultimately decides a placement, but viewability explains why some placements deliver clicks and impressions with no conversions: if the ads were barely viewable, the traffic that did come may be accidental or low-intent.
On the publishing side, an affiliate selling display or programmatic inventory on its own site should keep its placements genuinely viewable (above the fold or reliably in-view on scroll, not stacked or hidden), because advertisers and their verification vendors measure it and will cut or discount inventory that underperforms. The honest position is that viewability is a necessary quality floor, not a performance guarantee, and it should be read together with fraud filtering and the real downstream results.
Worked example
A buyer running display for a licensed operator sets a 70% minimum viewable rate and excludes any site below it after two weeks. Several cheap placements with high impression counts but sub-40% viewability are cut; spend moves to fewer, genuinely viewable placements, and cost per FTD improves even though the raw impression volume falls.
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