Viewability

Viewability is the measure of whether a served ad could be seen, judged against the Media Rating Council (MRC) standard for how much of the ad was on screen and for how long.

An impression is counted when an ad starts to load, which does not mean anyone could see it. The MRC's Viewable Ad Impression Measurement Guidelines, version 1.0 of 30 June 2014, set the rule most of the market uses. Display needs 50% of pixels on an in-focus browser tab for one continuous second. Video needs 50% for two continuous seconds. Large display ads of 242,500 pixels or more, the size of a 970x250 unit, may count at 30% of pixels (MRC, 30 June 2014).

Viewability is reported as a rate: viewable impressions divided by measurable impressions. Impressions a vendor cannot measure are neither viewable nor non-viewable, so a high rate on low measurability can mislead. Google's Active View, for example, applies the same 50% and one-second test to display ads (Google Ads Help, accessed 9 November 2026). Buyers who want to pay only for viewable impressions can buy on vCPM.

Viewability is a floor, not proof of attention. An ad can sit fully in view while the user looks elsewhere, which is why attention metrics emerged.

Example: In the ANA's Q2 2026 benchmark, the share of programmatic spend lost to non-viewable impressions fell from 13.3% to 10.1% in one quarter (ANA via Fiducia, 6 August 2026).

Related terms: vCPM, attention metrics, IVT, OM SDK, working media.

Authoritative source: Media Rating Council, Viewable Ad Impression Measurement Guidelines, version 1.0 (30 June 2014).

Read the full guide: Viewability, attention metrics and brand safety.