What is ad viewability and how is it measured?
The standard definition of a viewable impression, how viewability is measured, and what publishers can do to raise it and the price of their inventory.
Written by Samhub with the help of AI·Updated 13 Oct 2026·3 min readViewability measures whether an ad actually had a chance to be seen. By the common industry standard, a display ad counts as viewable when at least 50% of it is on screen for at least one continuous second. For video it is two seconds.
How viewability is measured
A script in the ad or ad server checks the ad’s position on screen. Viewability rate is the share of measured impressions that met the standard.
Viewability rate = viewable impressions ÷ measured impressions × 100
Example: 620,000 ÷ 1,000,000 × 100 = 62%
Illustrative numbers.
What is vCPM?
vCPM is the price per 1,000 viewable impressions. Buyers who pay by vCPM only pay for ads that met the standard, so publishers with high viewability can sell at a higher vCPM.
16 pages for publishers, with a checklist for data, programmatic and direct sales.
How to improve viewability
Place ads where people look
In-article and sticky placements beat units at the very bottom of the page.
Load ads when they are needed
Lazy loading requests the ad just before it scrolls into view.
Remove units nobody sees
Fewer, better placements raise both viewability and price.
Check speed
Slow pages lose readers before the ad loads.
CPM uplift at Stampen Media after activating first-party audiences with Samhub.
Frequently asked questions
Many buyers look for 70% or more. Compare by placement, because averages hide weak units.
No. It means the ad had a chance to be seen under the standard, not that the reader noticed it.
Ad servers and verification vendors. Buyers often use their own vendor, so numbers can differ slightly.
Yes. Buyers pay more for placements with high viewability, and some buy only viewable impressions.
Related terms
The price of 1,000 ad impressions.
The share of ad requests that get an ad.
Getting the most revenue from every impression.
The ad sizes every buyer and ad server supports.
The share of ad views that lead to a click.
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