What is an impression?
An impression is one instance of an ad being delivered and loaded on a screen, whether on a website, in an app, on a connected TV or on a digital billboard. It is the basic unit of digital advertising delivery: platforms count impressions to report how often an ad ran, and most programmatic media is priced per thousand impressions.
An impression does not mean someone saw or noticed the ad. That is why the industry also tracks viewable impressions and attention.
How impressions are counted
Under IAB and MRC measurement guidelines, a display impression is generally counted when the ad begins to load on the device, not merely when the server decides to send it. This is often called begin-to-render counting. Different systems can still report slightly different numbers because of timing, filtering and invalid traffic removal.
Served impression: the ad was delivered and started to render.
Viewable impression: the ad met the viewability standard. For display, that is at least 50% of pixels in view for one continuous second; for video, 50% of pixels for two continuous seconds.
Invalid impression: an impression flagged as bot or fraudulent traffic, which should be filtered out of billing.
Impressions and CPM
Most programmatic buying uses CPM, the cost per thousand impressions.
Cost = (impressions / 1,000) x CPM
For example, 400,000 impressions at a $5 CPM cost (400,000 / 1,000) x $5 = $2,000. If 70% of those were viewable, you got 280,000 viewable impressions, which works out to an effective viewable CPM of about $7.14.
Why impressions matter
Delivery tracking: impressions show whether a campaign is pacing to plan.
Pricing: they are the base for CPM and for calculating other costs, such as cost per click or cost per conversion.
Exposure control: impressions per user is the input for frequency capping.
Quality checks: comparing served, viewable and valid impressions reveals weak inventory.
Impressions are a volume measure, not a result. They tell you an ad loaded, not that anyone cared. A campaign with many cheap impressions can still perform poorly if they are low quality, hard to see or shown to the wrong people.
Impressions vs reach
Impressions count every time an ad is shown. Reach counts the number of unique people or households who saw it at least once. If 100,000 people each see an ad three times, that is 300,000 impressions and a reach of 100,000, with an average frequency of three. Impressions tell you how much you delivered; reach tells you how many people you delivered it to.
Impressions with AdGeeks
AdGeeks reports impressions alongside viewability, reach, frequency and outcomes, so volume is never read in isolation. On DV360, Amazon DSP and Adform, our traders shift budget away from placements with cheap but low-quality impressions toward ones that are seen and drive results. To get started, request access.
