viewability

Viewability is a metric used in digital advertising to indicate whether an ad had the opportunity to be seen by a user. It does not measure whether a user noticed the ad, but whether any portion of the ad was actually within the visible area of a browser window or app for a specified minimum duration. The most widely used thresholds are set by industry groups such as the Media Rating Council (MRC) and the Interactive Advertising Bureau (IAB). In display campaigns, an impression is considered viewable when 50% of the ad’s pixels are in view for at least one second; in video campaigns, 50% of the video’s pixels must be in view for at least two consecutive seconds.

Viewability is typically measured with client-side instrumentation that tracks viewport status, ad size, and scrolling. Vendors and platforms provide verification services by collecting data from the publisher site or app, sometimes combined with the IAB Open Measurement SDK to standardize measurements across mobile apps. Common providers include Integral Ad Science, DoubleVerify, and Moat, among others. Accreditation by bodies such as the MRC is often sought to certify measurement practices.

Why it matters: viewability affects the perceived effectiveness of campaigns, pricing, and inventory quality. Advertisers and agencies increasingly prefer viewable impressions, and some deals are priced or guaranteed on viewability metrics rather than served impressions.

Limitations include the fact that viewability is a proxy for exposure, not engagement; it can be influenced by ad placement, layout, and user behavior; fraud and non-human traffic remain concerns; cross-device measurement remains challenging.