What is viewability, and what does it not prove?
Part of Programmatic media planning
The short answer
Viewability says whether an ad had a chance to be seen. Under the Media Rating Council's guidelines, a display ad counts as viewable when at least 50 percent of its pixels are on screen for one continuous second, and a video ad when 50 percent are on screen for two continuous seconds. It measures the ad's position, not page quality.
Key takeaways
- The MRC sets the counting rule: 50 percent of pixels for one continuous second for display, and two continuous seconds of play for video.
- Large desktop display ads of 242,500 pixels or more need only 30 percent of pixels in view, and the mobile guidelines make no such exception.
- Read the viewable rate together with the measured rate, because impressions that could not be measured are left out of the viewable rate.
- Viewability describes the ad's condition on screen, regardless of whether a person looked at it or whether the page was worth reading.
- Before a deal, agree on the measurer, the environment split, any custom thresholds and whether price is set on served or viewable impressions.
What counts as a viewable impression for display and video?
Definition
- Viewable ad impression
- In the MRC's words, a served impression "can be classified as a viewable impression if the ad was contained in the viewable space of the browser window, on an in-focus browser tab, based on pre-established criteria such as the percent of ad pixels within the viewable space and the length of time the ad is in the viewable space of the browser."
The MRC Viewable Ad Impression Measurement Guidelines (opens in a new tab), version 2.0 of August 18, 2015, set the thresholds for desktop. The MRC Mobile Viewable Ad Impression Guidelines (opens in a new tab), final version of June 28, 2016, cover mobile web and apps. The desktop guideline says a viewable impression gives an opportunity to see the ad, "which may or may not be the case with a served ad impression." The thresholds are a floor for counting. The mobile guideline asks that custom thresholds above the minimum be "clearly disclosed and labeled in reporting," in addition to standard viewability reporting, not in lieu of it.
| Format and environment | Pixel requirement | Time requirement |
|---|---|---|
| Desktop display | At least 50 percent of the ad's pixels on an in-focus browser tab, in the viewable space | At least one continuous second, after the ad renders |
| Large desktop display, 242,500 pixels or more (the size of a 970 by 250 ad) | 30 percent of the ad's pixels in the viewable space | A minimum of one continuous second |
| Desktop video | 50 percent of the ad's pixels, not the player's | 2 continuous seconds of the ad played, not necessarily the first 2 |
| Mobile web and app display | 50 percent of density independent pixels, in an in-focus browser or a fully opened app | One continuous second, the same in news feeds and elsewhere |
| Large mobile display | No separate exception; the guideline asks for further study | One continuous second |
Order matters in the rule. The guideline says the pixel requirement comes first: "the clock starts on determining whether the ad meets the one continuous second time requirement only when the ad is determined to have met the 50% pixel threshold." A strong user interaction, such as a legitimate click, can also count an ad as viewable, but "a mouse-over alone generally would not," and impressions counted this way should be reported apart.
Who sets the viewability standard?
The standard comes from the Media Rating Council (opens in a new tab), which describes itself as "a not-for-profit industry self regulatory body, established in 1963 at the request of US Congress, that audits and accredits media measurement products and data sources." The desktop guideline was originally prepared with the IAB, and the MRC's standards listing (opens in a new tab) shows it issued in June 2014 and last updated in August 2015, with the mobile guideline issued in June 2016.
The MRC does two different things, and they are easy to merge. It publishes the guideline that defines a viewable impression, and it separately audits measurement services and accredits the ones that follow its rules. A service can measure viewability without accreditation, or be accredited for one environment, such as desktop display, and not another, such as in-app video. Buying platforms can adopt the same thresholds in their own reports: Google Ads, for example, counts a Display Network ad as viewable when "50 percent of your ad shows on screen for 1 second or longer," per its viewable CPM help page (opens in a new tab), checked October 2026.
How is viewability measured on a page?
How a measurer decides one impression is viewable
- Start from a valid served impression. Viewability sits on top of the normal impression rules; the mobile guideline notes a viewable impression must also be counted on the client side and "filtered for invalid activity."
- Check the pixels. Code attached to the ad, or in some methods to its container, checks how much of the ad sits in the visible part of the screen on a tab or app that has focus.
- Poll on a schedule. The desktop guideline requires checks at least every 100 milliseconds for display and every 200 milliseconds for video, which "equate to 10 consecutive positive observations for a viewable impression of either type."
- Start the clock only after the pixel test passes. One continuous second for display and two continuous seconds of play for video; time does not add up across separate glimpses.
- Sort every impression into a bucket. Viewable, non-viewable or undetermined, the three "mutually exclusive buckets" the guideline asks measurers to disclose.
Undetermined impressions are the part buyers overlook. Ads served into cross domain iframes can hide the page from the measuring code, and the guideline asks measurers to disclose how much they can see, "sometimes referred to as a 'see-through rate.'" That is why the MRC asks for three rates, reported together, and gives its own worked numbers: 1,000 rendered served impressions, of which 300 were viewable, 200 non-viewable and 500 undetermined.
| Rate | Formula in the guideline | Result in the MRC example |
|---|---|---|
| Measured rate | (Viewable + non-viewable) divided by total rendered served impressions | (300 + 200) / 1,000 = 50 percent |
| Viewable rate | Viewable divided by (viewable + non-viewable) | 300 / 500 = 60 percent |
| Impression distribution | Each bucket as a share of total rendered served impressions | 30 percent viewable, 20 percent non-viewable, 50 percent undetermined |
The guideline warns measurers not to call the 30 percent figure the viewable rate, since that "assumes that all undetermined were non-viewable." It also asks for desktop browser, mobile browser and mobile app results to be reported separately when a campaign spans them.
Why is viewability not the same as editorial quality?
Viewability is a statement about pixels and seconds. The IAB and MRC Attention Measurement Guidelines (opens in a new tab), published in November 2025, put the limit plainly: viewability considers "whether sufficient pixels of an ad are visible for a certain amount of time, representing the opportunity to see the ad," and it holds "regardless of whether or not the ad was seen, viewed or heard by a person." Nothing in the measurement reads the article around the ad.
The two can even pull in opposite directions. The ANA's 2023 release (opens in a new tab) found that made-for-advertising websites "exhibit high measurability rates, good viewability rates," which is one reason the guide to made-for-advertising sites treats a strong viewability report as no defense on its own. A specialist publisher with long articles may place ads lower in the page and post a modest viewable rate while being exactly where the brief belongs. Judge fit from the articles, then use viewability to compare slots and terms among sites that already fit.
What viewability questions should a buyer ask before a deal?
Viewability terms to settle before a deal goes live
- The measurer is named, and its accreditation covers this environment (desktop, mobile web or app) and format (display or video).
- Reports show the measured rate beside the viewable rate, so undetermined impressions are visible.
- Desktop, mobile web and app results are reported separately, as the guideline asks.
- Any threshold above the MRC minimum, such as 100 percent of pixels, is written into the deal and disclosed in reports.
- For large desktop units, both sides know whether the 30 percent rule for ads of 242,500 pixels or more applies.
- For video, the measurement uses the ad's pixels, not the player's, and two continuous seconds of the ad itself.
- Impressions counted as viewable through user interaction are reported apart from those meeting the pixel and time rule.
- The price basis is stated: served impressions, or viewable impressions only.
How does PlacementGraph look at ad layout before a site joins a plan?
What does a viewability discussion look like on one deal?
Fictional example
A Vancouver orchestra selling a concert season
A fictional Vancouver symphony orchestra wants display and short video ads in Vancouver and Victoria, in English, beside arts reviews, classical music features and city culture listings, to sell season subscriptions. Its agency plans a private auction with a regional arts and culture publisher already on the approved list.
The publisher's proposal quotes a viewable rate. The planner asks for the measured rate as well, a split between desktop, mobile web and the publisher's app, and the name of the measurer and what its accreditation covers. The reply shows the app inventory is measured by a different method from the web pages, so the desk asks for the two to be reported apart.
For the large desktop billboard unit, both sides confirm the 30 percent rule applies. The deal sheet records the measurer, the environment split, that pricing is on served impressions and that video is counted on two continuous seconds of the ad. The planner keeps the arts publisher on the list because of its reviews, not its viewability.
Frequently asked questions
Why do two measurement services report different viewability for the same campaign?
They can poll at different intervals, see through different iframes, and apply other filters before counting. The MRC desktop guideline notes that reductions from verification functions other than viewability "can result in unexplained inconsistencies in viewable impression reporting among measurers." Agree on one measurer of record in the deal, and compare measured rates before comparing viewable rates.
Does a click make an ad viewable?
It can. The MRC treats a legitimate click as a strong user interaction that may count an ad as viewable even when it missed the pixel and time rule, while a mouse-over alone generally does not qualify. A click that only starts a click to play video does not count by itself, and interaction based counts should be reported separately.
Do the same viewability rules apply to connected TV?
Not in the same form. The desktop and mobile guidelines cover browsers and mobile apps. The IAB and MRC attention guidelines of November 2025 summarize the MRC rule as 50 percent of pixels for one second for display or two seconds for video, and note 100 percent of pixels for cross-media measurement. Ask the seller which standard its connected TV reports follow.
Is a viewable impression the same as an attention measure?
No. The IAB and MRC attention guidelines describe attention as whether an ad was seen or heard by a person and to what depth, and they require a base of compliant viewable impressions before attention is measured. Viewability is the entry condition; attention measures what happened after it.
Sources
- Leading Trade Groups Define "Made For Advertising" Websites (September 26, 2023) (opens in a new tab)ANA
- Viewable Ad Impression Measurement Guidelines, version 2.0 (August 18, 2015) (opens in a new tab)Media Rating Council
- Mobile Viewable Ad Impression Measurement Guidelines (June 28, 2016) (opens in a new tab)Media Rating Council
- IAB and MRC Attention Measurement Guidelines, version 1.0 (November 2025) (opens in a new tab)IAB and Media Rating Council
- Standards and guidelines (opens in a new tab)Media Rating Council
- Media Rating Council home page (opens in a new tab)Media Rating Council
- Bid on viewable impressions using viewable CPM (opens in a new tab)Google Ads Help
Researched and written by PlacementGraph Research. Read how we research, source and update these pages. Corrections: diana@placementgraph.com.