Of every $1,000 that enters a demand-side platform, $150 buys impressions whose visibility was never determined. Not impressions that went unseen: impressions where nobody could establish whether they were seen at all. It is the single largest leak in the programmatic chain, ahead of demand-side platform fees, ahead of supply-side platform fees, ahead of fraud by a factor of thirty.

It appears on no campaign report, because the metric that would expose it is almost never displayed next to the one everybody looks at.

Two rates, two denominators, one of them displayed

The standard sorts impressions into three categories it calls mutually exclusive: viewable, non-viewable, and viewable status undetermined. That third category is not a quality judgment. It is the absence of a verdict:

“Undetermined Ad Impression: These represent served impressions where the viewable status cannot be determined because of any conditions that do not allow that decision to be made. For example: (1) if cross-domain I-Frames block the viewable determination, (2) clients not supporting Java script, and/or (3) any other issues where browser settings or serving conditions disallow verification of the ad position on the page or the time-viewed.”

From this follow two rates:

  • The measured rate divides measured impressions by total served.
  • The viewable rate divides viewable impressions by measured ones only.

The standard supplies its own worked example, and it is instructive. One thousand impressions: 300 viewable, 200 non-viewable, 500 undetermined.

The measured rate is 50%. The displayed viewable rate is 60%, because it is computed across the 500 impressions anyone managed to observe. The share genuinely viewable across the whole campaign is 30%.

The document then forbids calling that 30% the viewable rate:

“Viewable Ad Impression measurers should not refer to the 30% in the Impression Distribution category as the ‘Viewable Rate’ since it assumes that all undetermined were non-viewable, thought to be an overly conservative presentation.”

The reasoning is defensible: nobody knows whether the undetermined impressions were viewable, so counting them as failures would be unfair. The practical result is that a report can accurately claim 60% viewability on a campaign where the fate of half the impressions is unknown.

On real data the gap is comparable. A study covering 21 advertisers and 35.5 billion impressions found median measurability of 86% and viewability of 85% among measured impressions. Multiplying gives the only honest figure:

“Given that 86 percent of total impressions were measurable and 85 percent of measurable impressions were viewable, only 73 percent of total impressions were both measurable and viewable.”

With enormous dispersion between advertisers: measurability ran from 0.02% to 99.61%, and four participants sat below 20%.

The two advertising viewability rates and the difference in denominator between themThe two advertising viewability rates and the difference in denominator between them, illustrated with the worked example contained in the measurement standard itself. The standard sorts impressions into three mutually exclusive categories: viewable impressions, non viewable served impressions, and impressions whose viewable status is undetermined, this last category covering served impressions whose viewable status could not be determined because of conditions preventing that decision, for example cross domain inline frames blocking the determination, clients not supporting the scripting language, or any other browser settings or serving conditions that disallow verification of the ad position on the page or of the time viewed. On an example of one thousand rendered impressions comprising three hundred viewable, two hundred non viewable and five hundred of undetermined status, the measured rate, computed by dividing the sum of viewable and non viewable impressions by total rendered served impressions, is fifty percent. The viewable rate, computed by dividing viewable impressions by the sum of viewable and non viewable impressions only, is sixty percent. The impression distribution, which expresses each category as a share of total rendered impressions, gives thirty percent viewable, twenty percent non viewable and fifty percent undetermined. The standard expressly states that measurers should not refer to the thirty percent figure as the viewable rate, on the ground that doing so assumes all undetermined impressions were non viewable, which it describes as an overly conservative presentation. On real data from a study covering twenty one advertisers and thirty five point five billion impressions, median measurability is eighty six percent and viewability among measured impressions is eighty five percent, so that only seventy three percent of total impressions were both measurable and viewable, with individual measurability rates ranging from two hundredths of one percent to ninety nine point six one percent and four advertisers below twenty percent.One thousand impressions, two rates, two answersViewable300Non-viewable200Status undetermined500Viewable rate300 of (300 + 200)60%this is the one you seeGenuinely viewable share300 of 1,00030%and calling it the “viewablerate” is forbiddenOn real data, 21 advertisers: 86% measurability, 85% viewability among measured impressions,so 73% of impressions were both measured and viewable. From 0.02% to 99.61% by advertiser.
The same thousand impressions yield 60% or 30% depending on the denominator. Only one of the two gets displayed. Source : MRC, Viewable Ad Impression Measurement Guidelines v2.0, 18 August 2015, pages 12 and 13; ANA, Programmatic Media Supply Chain Transparency Study, December 2023, page 87 (2015)

Why it cannot be measured

Three causes, all documented.

Cross-domain iframes. An ad served inside an iframe whose domain differs from the host page cannot, for browser security reasons, query the geometry of the parent document. The measurement script is there and it runs, but it cannot establish where the ad sits on screen. The standard devotes a section to this and creates a dedicated metric, the see-through rate, to quantify how far a measurer can see into nested frames. An advisory published in 2012, based on a pilot covering 22 campaigns and more than three billion served impressions, already put a number on it: cross-domain iframes accounted for three quarters of unmeasured impressions in network placements, and measured rates in that pilot ran at 27% for publisher placements and 19% across ad networks.

Environments without scripting. Some video players and platforms do not execute JavaScript. The study adds a fourth reality to the technical list: placements where the seller has simply rejected the verification tags.

Apps and connected television. This is the most radical case, because the definition of viewability loses its meaning entirely: “50% of pixels in the viewable space of the browser tab” says nothing about a television set. The standard concedes the point:

“OTT often cannot be measured in the same way as traditional digital video delivery due to limitations on JavaScript and SDK in OTT environments, as well as additional challenges such as TV Off detection.”

What replaces pixel measurement there are state checks: detecting that the screen is off while the device stays active, detecting continuous play with nobody in the room. A standardized measurement SDK exists for apps, but its announced connected-TV coverage was still 40% of the market in May 2024, after extension to two major manufacturers.

The three documented causes making an advertising impression unmeasurableThe three documented causes making an advertising impression unmeasurable, according to the measurement standards and the advertiser association study. The first cause is the cross domain inline frame: when an advertisement is served inside a frame whose domain differs from that of the host page, browser security restrictions prevent the measurement script from querying the geometry of the parent document, so the script executes but cannot determine the position of the advertisement on screen. The standard devotes a section to this problem, describes frames nested within one another creating a chain of serving instances, and introduces a dedicated metric called the see through rate to quantify how far the measurer can see into those frames. An advisory published in November two thousand twelve, based on a pilot covering twenty two campaigns and more than three billion served impressions, established that cross domain frames accounted for three quarters of unmeasured impressions on advertising network placements and more than a third on publisher placements, with overall measured impression rates then standing at twenty seven percent for publisher placements and nineteen percent across ad network placements. The second cause is the absence of a scripting environment: some video players and platforms do not execute the scripting language, and the standard explicitly cites clients not supporting that language among the conditions rendering status undetermined, while the study adds the case of placements where the seller has rejected the verification tags. The third cause concerns applications and connected television, where the very definition of viewability loses its meaning because the notion of a percentage of pixels within the viewable space of a browser tab has no significance on a television set; the standard concedes that television delivered over the top often cannot be measured in the same way as traditional digital video delivery because of limitations on the scripting language and on software development kits in those environments, as well as additional challenges such as detecting that the television is switched off. In that environment pixel measurement is replaced by state checks, consisting of detecting that the screen is off while the device remains active, and of ending abnormally long sessions in the absence of interaction. A standardized measurement kit exists for applications, whose announced coverage of connected television was forty percent of the household market in May two thousand twenty four after extension to two major television manufacturers.Three reasons never to knowThe cross-domain iframeThe browser forbids the script from seeing the parent page. It runs blind.In 2012: three quarters of unmeasured impressions on network placements.No scriptingSome video players do not run it. Some sellers reject the verification tags outright.Without a script, no measurement is possible.The app and the television”50% of pixels in the browser tab” means nothing on a TV set.The standardized kit covered 40% of the household market in May 2024.
The script is present and running. It simply cannot see where the ad is. Source : MRC, Viewable Ad Impression Measurement Guidelines v2.0, 2015; MRC, Viewable Impression Advisory, 14 November 2012; MRC, Server-side Ad Insertion and OTT Guidance, August 2021; ANA, December 2023, page 86; IAB Tech Lab, Open Measurement SDK (2021)

Why this line costs more than the fees

The $150 deserves breaking down, because how it forms explains why it goes unnoticed.

The non-measurable line represents 14% of impressions but 21.5% of spend. The study gives the reason:

“Video as a format over-indexes for non-measurable inventory, and also has higher CPMs resulting in the delta we see here of 14 percent of impressions but 21.5 percent of spend.”

The problem concentrates exactly where the thousand costs most. You lose proportionally more money than impressions, which makes the line invisible to anyone reasoning in volume.

Against the other lines in the same waterfall, on $1,000 entering the demand-side platform: DSP platform fees $80, DSP additional fees $20, data fees $60, SSP platform fees $130. Then, against seller revenue: non-viewable $95, invalid traffic $5, non-measurable $150, made-for-advertising inventory $100.

The non-measurable line is the heaviest in the entire chain, ahead of the largest platform fee. And unlike the fees, it appears on no invoice.

Weight of the non measurable line compared with every other line in the programmatic chainWeight of the non measurable line compared with every other line in the programmatic chain, on a base of one thousand dollars entering a demand side platform. Transaction costs account for twenty nine percent of the advertising dollar and break down into eighty dollars of demand side platform fees, twenty dollars of additional demand side platform fees, sixty dollars of data fees, and one hundred and thirty dollars of supply side platform fees, leaving seven hundred and ten dollars of seller revenue. Loss of media productivity then accounts for thirty five percent of the advertising dollar and breaks down, calculated against that seller revenue, into ninety five dollars of non viewable impressions, five dollars of invalid traffic, one hundred and fifty dollars of non measurable impressions, and one hundred dollars of spend on made for advertising sites. The non measurable line is therefore the heaviest in the entire chain, larger than the highest fee line which is supply side platform fees at one hundred and thirty dollars, and it is the only line in the list that appears on no invoice. How it forms explains why it goes unnoticed: it represents fourteen percent of impressions but twenty one and a half percent of spend, a gap the study attributes to video over indexing for non measurable inventory while also carrying higher costs per thousand. The detailed calculation in the study appendix multiplies each category’s share of total advertising spend by the seller revenue share of seventy one percent, giving for the non measurable line twenty one and a half percent multiplied by seventy one percent equals fifteen percent, or one hundred and fifty dollars per thousand.Per $1,000 invested, line by lineWhat shows up on an invoiceSupply-side platform$130Demand-side platform$80Data$60Additional platform fees$20What shows up nowhereNon-measurable$150Made-for-advertising inventory$100Non-viewable$95Invalid traffic$5
The only line here that appears on no invoice is also the largest. Source : ANA, Programmatic Media Supply Chain Transparency Study, December 2023, pages 99 to 101 and 121 (2023)

And if the threshold itself means nothing?

There is a question nobody asks: does an impression that is “viewable” under the standard, meaning 50% of pixels for one second, produce anything at all?

Where the threshold came from. Not from a study of perception. From a negotiation among three trade associations in 2012, validated by a pilot covering 22 campaigns and over three billion served impressions. The standards body’s own executive has explained the reasoning publicly: the threshold was adopted because 80% of display ads meeting it would also have qualified under the stricter criterion of 100% of pixels in view for a second. That is a calibration between two measurement methods, not a duration validated as sufficient to produce an effect. The stated motivation on the trade side was equally practical: create a currency “that can get brands excited about investing in digital”.

What the research says. The only published causal experiment on exposure duration and memory, in the proceedings of an ACM conference, tests no duration shorter than five seconds. The regulatory threshold of one second therefore sits entirely below the range anyone has examined. The authors report that recall and recognition “increases sharply in the first 10 seconds”.

And the two studies that tested the threshold disagree. A randomized experiment, which remains a working paper and to my knowledge was never published in a peer-reviewed journal, concludes that “everything below 75% or 5 seconds seems to perform a lot worse”, and that “advertisers will have to understand that the MRC standard is not enough from an advertising effectiveness stance”. Its authors note that their own observational analysis of the same data suggested the opposite, and attribute the discrepancy to endogeneity bias. A 2025 article in the Journal of Advertising reaches the contrary conclusion, finding concurrent validity between the one-second threshold and attention measured by mobile eye-tracking, plus predictive validity for brand recall.

What a 2025 causal study in the Journal of Marketing Research does establish, on 1,013 participants with webcam eye-tracking: one additional second of actual attention raises the probability of recall by 3.4 percentage points and the probability of choosing the brand by 0.7 points. Note the difference: that is seconds of real gaze, not the crossing of a declarative threshold.

There is a broader reason to hold all of this loosely. Twenty-five large-scale field experiments published in the Quarterly Journal of Economics found that “the median confidence interval on return on investment is over 100 percentage points wide”, and that detecting a 10% difference in advertising ROI would require campaigns roughly sixty times larger than those typically run. The authors are blunt about why observational methods fail here: “selection bias, due to the targeted nature of advertising, is a crippling concern for widely employed observational methods.” A separate field experiment published in Econometrica measured the gap directly: standard regression put the return on paid search at over 4,100%, while the experimental estimate was -63%.

Fourteen years into using viewability as a transactional currency, there is no scientific consensus on whether it predicts anything.

Origin of the viewability threshold and the state of research on its validityOrigin of the viewability threshold and the state of research on its validity. The standard requires that at least fifty percent of an advertisement’s pixels be viewable for at least one continuous second for display, and two continuous seconds for video. That threshold did not come from a study of perception or memory but from a negotiation among three trade associations begun in twenty eleven and validated by a feasibility pilot conducted in spring twenty twelve across twenty two campaigns representing more than three billion served impressions. The standards body’s executive has publicly explained that the threshold was adopted because eighty percent of display advertisements meeting it would also be considered viewable under the stricter criterion of one hundred percent of pixels in view for one second, making it a calibration between two measurement methods rather than a duration empirically validated as sufficient to produce a cognitive or commercial effect. The standard itself describes the viewable impression as an opportunity to see, noting that such an opportunity exists with a viewable impression, which may or may not be the case with a merely served impression. On the research side, the only published causal experiment on the relationship between exposure duration and memory, appearing in the proceedings of a computing association conference in twenty eleven, tests no duration shorter than five seconds in its exogenous exposure protocol, placing the one second regulatory threshold entirely below the range examined; its authors report that the combined recall and recognition measure increases sharply during the first ten seconds and continues rising more slowly thereafter. A later randomized experiment, which remains a working paper whose publication in a peer reviewed journal has not been confirmed, concludes that everything below seventy five percent of pixels or five seconds performs considerably worse on recognition, its authors writing that advertisers will have to understand that the standard is not enough from an advertising effectiveness standpoint, and noting that their own observational analysis of the same data suggested the opposite, a discrepancy they attribute to endogeneity bias. A peer reviewed article published in twenty twenty five concludes to the contrary that the one second threshold shows concurrent validity with attention measured by mobile eye tracking and predictive validity for brand recall. What is established by a causal study published in a peer reviewed journal the same year, based on a randomized experiment with one thousand and thirteen participants using webcam eye tracking, is that one additional second of attention actually paid to a brand’s advertisement raises the probability of recall by three point four percentage points and the probability of choosing that brand’s voucher over cash by seven tenths of a point. More broadly, twenty five large scale field experiments published in an economics journal found that the median confidence interval on advertising return on investment exceeds one hundred percentage points in width, and that detecting a ten percent difference in return would require campaigns approximately sixty times larger than those typically run, with selection bias described as a crippling concern for widely employed observational methods; a separate field experiment published in an econometrics journal measured a standard regression estimate of over four thousand one hundred percent return on paid search against an experimental estimate of minus sixty three percent.Where “50% of pixels, one second” came from2012, a negotiation among three trade bodiesAdopted because 80% of ads meeting it also qualified under a stricter criterion.What the research saysCausal exposure study, 2011tests nothing under 5 secondsRandomized experiment, working paperthe threshold is not enoughPeer-reviewed article, 2025the one-second threshold is validWhat is established, on seconds of gaze actually measuredOne more second of attention: +3.4 points of recall, +0.7 points on brand choice.Not the crossing of a threshold. Actual looking.
A calibration between measurement methods. Research has never validated it, and does not agree. Source : MRC, Viewable Impression Advisory, 14 November 2012; Goldstein, McAfee and Suri, ACM Conference on Electronic Commerce, 2011; Uhl, Abou Nabout and Miller, working paper, 2020; Simonov, Valletti and Veiga, Journal of Marketing Research 62(2), 2025; Lewis and Rao, Quarterly Journal of Economics 130(4), 2015; Blake, Nosko and Tadelis, Econometrica 83(1), 2015 (2025)

The November 2025 admission

There is a way to settle the debate without taking sides: look at what the bodies that created the measure are now doing.

In November 2025, the IAB and the MRC jointly published an entirely new framework, devoted to measuring attention. Building a further measurement layer fourteen years after making viewability a trading currency is itself an answer. The document carries a caution the viewability standard never had:

“Attention is not intended to serve as a standalone measure of ad effectiveness of business results.”

And it explicitly files viewability under delivery verification, alongside impression counting, rather than under quality or effect measurement.

That classification is not new. It was implicit in the original definition of the viewable impression:

“It is recognized that an ‘opportunity to see’ the ad exists with a viewable ad impression, which may or may not be the case with a served ad impression.”

An opportunity to be seen. The body that built the metric never claimed it established that anyone had seen anything.

What the viewability measure establishes according to the bodies that created itWhat the viewability measure establishes according to the standards bodies that created it. In the founding document defining the viewable impression, the standards body states that it is recognized that an opportunity to see the advertisement exists with a viewable ad impression, which may or may not be the case with a served ad impression. The measure therefore establishes an opportunity to be seen, and not the fact that any person actually saw the advertisement. In November two thousand twenty five, fourteen years after making viewability a trading currency, the two reference bodies of the sector jointly published an entirely new framework devoted to the measurement of attention. That document states that attention is not intended to serve as a standalone measure of advertising effectiveness or business results, that attention in and of itself should not be considered or used as a measure of outcomes for the purpose of evaluating campaign performance, and that the guidelines strongly require validation for models and measurement approaches, strongly encouraging that attention’s potential impact on and correlation with outcomes be subject to rigorous empirical support, validation and independent audit. The same document excludes from its scope techniques and tools focused solely on delivery verification, a category in which it explicitly places basic ad serving, impression counting, and viewability, audibility and user presence signals. Viewability is therefore filed by the standard itself under delivery verification rather than under quality or effect measurement. Finally, on the supposed remedy of buying on a viewable cost per thousand basis, the official documentation of a major platform states that a small portion of served impressions might be charged in that mode, so that this billing method excludes impressions measured as non viewable but does not guarantee excluding those whose viewability could never be determined.What the measure establishes, per its authorsIn the founding text”It is recognized that an ‘opportunity to see’ the ad exists with a viewable ad impression”An opportunity. Not a viewing.In the November 2025 frameworkViewability is filed under “delivery verification”, next to impression counting.Not under quality measurement. Not under effect measurement.And on the supposed remedyBuying on viewable CPM: “A small portion of served impressions might be charged.”You exclude the measured non-viewable, not the never-measured.
An opportunity to see, filed by the standard itself under delivery verification. Not under media quality. Source : MRC, Viewable Ad Impression Measurement Guidelines, June 2014 and v2.0 August 2015; IAB and MRC, Attention Measurement Guidelines, Final Version 1.0, November 2025; Google Ads Help, Bid on viewable impressions using viewable CPM (2025)

What to do

Ask for the measured rate alongside the viewable rate. This is the one action here that costs nothing and changes everything. A viewability figure without its measurability figure is uninterpretable, and the standards body publishes both formulas precisely so they are read together.

Multiply the two. 86% measurability and 85% viewability do not make 85%. They make 73%. That is the number describing your campaign.

Treat video separately. That is where the non-measurable concentrates, and where the thousand costs most. A report aggregating display and video hides the problem by construction.

Do not expect viewable CPM to fix it. Google’s documentation is explicit that in that mode “a small portion of served impressions might be charged”.

Select for publishers that accept verification tags. The study’s recommendation is to prioritize them, aiming for 100% of impressions to be measurable, and to pay only for measurable impressions. That is an inventory selection criterion, not a technical setting, and it is negotiable. It is one of the constraints we buy under, which is why our B2B paid acquisition work is judged on cost per lead rather than on thousands of impressions delivered.

One closing caution, less advice than a reading instruction. Even at 100% measurability and 100% viewability, you will not have shown that anyone looked at your ad. You will have shown it was delivered under conditions where looking was possible. That is useful, it is necessary, and it is not the same thing.