What is viewability?

Viewability is a digital advertising metric that shows whether an ad had a real chance to be seen by a user. Instead of counting every loaded impression, viewability focuses on impressions that were actually visible on screen for long enough to register.

In programmatic and display advertising, viewability is usually expressed as a percentage. It is calculated as viewable impressions divided by all measurable impressions. Most platforms follow industry guidelines, for example an ad is viewable when at least 50 percent of its pixels were in view for at least one second for display, or two seconds for video.

Why viewability matters for performance

Viewability matters because you do not want to pay for impressions that nobody could see. If your ads load below the fold and users scroll past too fast, you get impressions without attention. A strong viewability rate helps you protect budget, improve campaign efficiency, and get more reliable data on what creatives and audiences work.

For e commerce and B2B brands that invest heavily in programmatic display and video, viewability is a core quality metric. It directly influences other KPIs like click through rate, cost per acquisition, and brand lift, since an invisible ad cannot be clicked or remembered.

How viewability is measured

Viewability is measured with tracking scripts or SDKs that run in the user’s browser or app. These tools check if the ad is within the visible area of the screen, how many pixels are in view, and for how long. The result is a simple percentage that you can use next to CPM, CPC, and conversion metrics.

In a typical dashboard, you might see:

  • Viewability rate Percentage of measurable impressions that were viewable.
  • Viewable CPM Effective cost per thousand viewable impressions, not just served ones.
  • Viewable impressions The absolute number of impressions that met the viewability standard.
  • Breakdowns Viewability by placement, device, format, publisher, or creative.

Together, these numbers help you spot weak placements, negotiate better inventory, and shift spend to formats that actually get seen.

What affects viewability?

Several factors influence viewability. Ad position is a big one, with above the fold slots usually delivering higher viewability than units buried at the bottom of a page. Page layout, loading speed, lazy loading scripts, and user behavior such as fast scrolling also play a role.

Your buying setup matters too. Working with a capable demand side platform (DSP) and high quality supply via an SSP in programmatic advertising gives you more control over inventory quality. Adding stricter inclusion lists and other safeguards, explained in detail in guides on whitelists in programmatic, can further protect viewability.

Using viewability to optimise campaigns

To use viewability well, do not look at it in isolation. Combine viewability data with cost metrics like CPM, which we cover in depth in our guide on what CPM means in programmatic, and with business outcomes such as leads or revenue. Sometimes a slightly lower viewability placement can still win if it delivers cheaper conversions.

For growth minded teams, viewability is a practical lever, not a vanity metric. Use it to refine placements, creative formats, and frequency, and to make sure every impression you buy has a fair chance to move prospects closer to a click, a lead, or a sale.