Why Viewability Matters
An impression can be technically “served” without ever actually appearing on a viewer's screen — loaded far down a page the visitor never scrolled to, for example. Viewability rate measures what share of impressions met a minimum visibility standard, separating ads that had a real chance of being seen from ones that didn't.
See CPM vs vCPM for how viewability feeds into pricing specifically.
Viewability Rate Formula
Divide viewable impressions by total impressions, then multiply by 100.
Viewability Rate = (Viewable Impressions ÷ Total Impressions) × 100
Worked Example
A placement serves 500,000 impressions, of which 350,000 meet the viewability standard.
Viewability Rate = (350,000 ÷ 500,000) × 100 = 70%
What Affects Viewability?
- Ad placement on the page — above-the-fold units are naturally more likely to be seen than ones deep in a long page.
- Page load speed — slow pages can cause visitors to leave before an ad lower on the page ever renders.
- Ad size and format — larger, more prominent formats are harder to scroll past without at least partially viewing.
- Device type — mobile and desktop viewability often differ due to screen size and typical scrolling behavior.
Viewability Rate Calculator FAQ
How is viewability rate calculated?
Viewability rate is calculated by dividing viewable impressions by total impressions, then multiplying by 100: Viewability Rate = (Viewable Impressions ÷ Total Impressions) × 100. Enter your figures above to calculate it instantly.
What counts as a "viewable" impression?
The Media Rating Council's common standard requires at least 50% of a display ad's pixels to be on screen for a minimum of one second (two seconds for video). An ad that loads but is never scrolled into view, or is only briefly visible, doesn't count as viewable even though it still counts as a served impression.
What's a good viewability rate?
Many buyers treat 70% as a reasonable benchmark for display, though expectations vary by format and placement. Compare your viewability rate against your own historical placements and the specific standard your buyer or platform uses.
Does low viewability mean wasted ad spend?
Largely yes for impression-based pricing — an ad that was never actually visible had essentially no chance to be seen, regardless of what it cost. This is why some buyers specifically price or guarantee on viewable impressions (vCPM) rather than raw served impressions.