What is a good viewability rate?

Around 70% is a common contractual floor for display, and premium placements clear it comfortably. But the number is meaningless without the measurement rate beside it — 80% viewability on 40% of impressions tells you much less than 65% viewability on 95% of them.

Why do my verification vendor and my ad server disagree?

Because they count different things at different moments. The ad server counts what it served; the vendor counts what its tag could measure and assess. A gap of several percent is routine. Pick one as the source of truth for billing and state which in the insertion order.

Does a viewable impression mean someone saw the ad?

No. It means the pixels met a geometric threshold for a length of time. It is a measure of opportunity to see, not of attention. That is precisely why attention metrics emerged as a separate category — viewability sets a floor, it does not describe engagement.

Viewability Calculator

Calculate viewability rate from viewable and measured impressions. The arithmetic is one division; the difficulty is that three different impression counts are in play, and picking the wrong denominator quietly changes the answer by ten points or more.

Viewable impressions

Measured impressions

Viewability

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Enter both figures to calculate.

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Formula

Viewability Rate = (Viewable Impressions ÷ Measured Impressions) × 100

The denominator is measured impressions, not served impressions. Using served in its place is the single most common way a viewability figure ends up wrong — and it always understates the result.

Measured is not the same as served

Every campaign has three impression numbers. Served impressions are what the ad server delivered. Measured impressions are the subset a verification vendor could actually assess — some environments block measurement, so this is always lower. Viewable impressions are the subset of measured ones that met the standard. Viewability rate divides viewable by measured, and if you divide by served instead you are penalising the campaign for impressions nobody could measure. The gap between served and measured is the measurement rate, and it deserves reporting alongside viewability rather than being buried.

What actually counts as viewable

The MRC standard for display is at least 50% of the ad's pixels in view for at least one continuous second. Video is stricter on time and looser on nothing: 50% of pixels for at least two continuous seconds. Large display units above 242,500 pixels use 30% for one second instead, since a billboard rarely fits half its area on screen at once. These thresholds matter when comparing vendors — two verification providers measuring the same campaign will not agree exactly, and a few points of difference between them is normal rather than evidence that one is wrong.

Frequently asked questions

What is a good viewability rate?: Around 70% is a common contractual floor for display, and premium placements clear it comfortably. But the number is meaningless without the measurement rate beside it — 80% viewability on 40% of impressions tells you much less than 65% viewability on 95% of them.
Why do my verification vendor and my ad server disagree?: Because they count different things at different moments. The ad server counts what it served; the vendor counts what its tag could measure and assess. A gap of several percent is routine. Pick one as the source of truth for billing and state which in the insertion order.
Does a viewable impression mean someone saw the ad?: No. It means the pixels met a geometric threshold for a length of time. It is a measure of opportunity to see, not of attention. That is precisely why attention metrics emerged as a separate category — viewability sets a floor, it does not describe engagement.