Viewability
A metric measuring whether a digital ad was actually visible to a user, as defined by industry standards for pixel exposure and time on screen.
Definition
Viewability is an advertising metric that determines whether a served ad impression was actually visible to a human viewer. The Media Rating Council defines a viewable display ad as one where at least 50% of its pixels are visible in the browser viewport for a minimum of one continuous second. For video ads, the threshold is 50% of pixels visible for at least two continuous seconds.
Viewability addresses the reality that many served impressions never actually reach human eyes — ads may load below the fold where users never scroll, in background browser tabs, or in positions that are technically rendered but practically invisible.
Why It Matters
Paying for ad impressions that nobody sees is a waste of marketing budget. Viewability metrics give advertisers the data they need to evaluate placement quality and negotiate performance-based pricing. Many advertisers now require minimum viewability thresholds in their media contracts.
High viewability rates correlate with better campaign outcomes. Ads that are actually seen by users naturally generate higher brand awareness, engagement, and conversion rates than impressions that exist only as server logs.
Examples in Practice
An advertiser sets a 70% viewability threshold for their programmatic campaigns, meaning they only pay for placements where at least 70% of served impressions meet the MRC viewability standard.
A publisher redesigns their page layout to move ad units above the fold and implement lazy loading, increasing their average viewability rate from 48% to 72%, which commands higher CPMs from advertisers.
A brand compares viewability rates across different ad exchanges and discovers that one exchange consistently delivers below 40% viewability, prompting them to reallocate that budget.