An ad that loads but is never seen earns little and teaches buyers to bid less for that slot. Viewability is the measure of whether an ad had a real chance to be seen. It is reported in almost every ad platform, but it is easy to misread, and the most obvious way to raise it, removing ad slots, can lower revenue.
What counts as a viewable impression
The widely used industry guideline, issued by the Media Rating Council (MRC) with the IAB, defines a viewable impression as:
- Display ads: at least 50% of the ad's pixels in view for at least one continuous second.
- Large display ads (242,500 pixels or more, such as a 970×250 billboard): at least 30% of pixels in view for one continuous second.
- Video ads: at least 50% of pixels in view for at least two continuous seconds.
"Continuous" matters. An ad that is half in view for half a second, scrolls away, then comes back for another half second has not met the standard. Google's Active View measurement, used in AdSense and Ad Manager reporting, is based on these same thresholds. The Media Rating Council publishes the underlying guidelines.
Read the transcript
What counts as a viewable ad? For display ads, at least half of the ad's pixels must be on screen for at least one continuous second. Let's watch two visits to the same page. On the first visit, the reader scrolls past quickly. The ad is more than half in view for only about half a second. It never reaches one second, so it doesn't count as viewable. On the second visit, the reader stops to read. The ad stays more than half in view, and after one continuous second, it counts as a viewable impression. There are two variations. Large display ads need thirty percent of their pixels in view for one second. Video ads need half their pixels in view for two continuous seconds.
How the rate is calculated
Viewability rate is viewable impressions divided by measurable impressions, not by all impressions. Some impressions cannot be measured, for example because of how the creative is served or the environment it loads in. Always look at the measurable rate alongside the viewability rate. A high viewability rate on a small share of measurable impressions tells you less than it seems.
In Google Ad Manager the relevant metrics include Active View viewable impressions, Active View measurable impressions, Active View percentage viewable and average viewable time. AdSense reports Active View viewable as well. Other partners use their own measurement, so expect some differences between reports.
Why viewability affects revenue
- Buyers predict it. Many buyers estimate how likely an impression is to be seen and adjust their bids. Slots with a history of low viewability can attract lower bids.
- Some campaigns only pay for viewable impressions. If a slot is rarely seen, it cannot earn from those campaigns.
- Unseen ads still cost you. Every ad request adds page weight and work in the browser, whether or not anyone sees the ad.
Diagnose by placement and device
A site-wide viewability rate hides the useful detail. Break it down by ad slot, device and page template, and look at the number of viewable impressions per page view as well as the rate.
| Placement | Common pattern | What to check |
|---|---|---|
| Top of page, above the header or first heading | Loads first, but readers often scroll past it before it renders | How long the ad takes to render; whether the slot is reserved so it does not shift content |
| In-content, between paragraphs | Often among the better performers because readers slow down to read | Spacing between units; whether they are lazy loaded close enough to the reader |
| Desktop sidebar | The first unit can be seen; lower units scroll away quickly | Whether a sticky sidebar unit would replace several static ones |
| Below the article, comments or footer | Frequently low, because many readers never get there | Scroll depth on that template; whether the slot earns its page weight |
| Anchor or sticky units | Usually high, because they stay on screen | Partner and platform policies, and how readers respond to them |
Ways to improve viewability
- Lazy load below-the-fold slots. Request and render ads shortly before they scroll into view instead of on page load. Google Publisher Tag supports this with
enableLazyLoad, which has separate margins for fetching and rendering and a multiplier for mobile. See the Google Publisher Tag reference. Too small a margin and the slot is empty when it arrives; too large and you lose the benefit. - Place ads where people pause. In-content positions near the parts of a page people read usually do better than positions at the edges.
- Use sticky units carefully. A single sticky sidebar unit can replace several low-viewability static ones on desktop.
- Make ads render faster. Faster auctions and lighter pages mean the ad is in place while the reader is still looking. See our guides on header bidding timeouts and Core Web Vitals and ads.
- Refresh only what is being seen. If you refresh ads, refresh only slots that are in view and have been for a while, follow each partner's rules on refresh, and declare refreshed inventory where your ad platform requires it.
- Remove slots that never earn their place, but only after checking the revenue they bring.
The trade-off to watch
Viewability rate and revenue do not always move together. Removing a low-viewability slot raises the rate immediately, but it also removes that slot's revenue. The question is whether the remaining slots earn enough more to make up for it. Track these together:
- Viewable impressions per page view
- Page RPM (revenue per 1,000 page views)
- Viewability rate and measurable rate by slot
- Page speed and layout stability
What not to do
- Do not hide, stack or overlap ads to inflate impressions or viewability. Ad platform policies prohibit it and it risks your account.
- Do not refresh ads that are out of view or refresh on a short timer regardless of what the reader is doing.
- Do not judge a change on viewability rate alone.
Common questions
What is a good viewability rate?
It depends on your layout, audience and the mix of devices. Compare your own slots with each other and over time, and focus on the number of viewable impressions per page view and on revenue, rather than a single target number.
Why is my viewability different in each partner's report?
Partners use different measurement methods and can only measure the impressions they serve. Some impressions are not measurable at all. Compare like with like, and check the measurable rate before comparing viewability rates.
Does lazy loading always improve revenue?
Not always. It usually improves viewability and page speed, but it can reduce the number of impressions per page view. Test the margins and compare page RPM before and after.
Is a sticky ad always a good idea?
Sticky units often have high viewability, but they take space on the screen and are subject to platform policies and reader tolerance. Test them, keep them small on mobile, and check each partner's rules.