Reference library · Media planning
Impressions
Impressions are the total count of times an ad is served or displayed, tallied on every load regardless of whether the same person sees it more than once. A single person exposed five times generates five impressions. Impressions are the base delivery currency for CPM buying and the raw input from which reach and frequency are calculated.
Formula
Worked example
A display campaign targeting Warsaw and Krakow reaches 600,000 unique users at an average frequency of 4: 600,000 x 4 = 2,400,000 impressions delivered over the two-week flight. At a €4.20 CPM that volume costs 2,400,000 / 1,000 x €4.20 = €10,080, which is the number the planner checks against the media budget before confirming the buy.
How it is used
Planners forecast impressions during sizing to set the CPM budget, then track delivered impressions daily against the flight pacing goal, reconciling ad-server or verification-vendor counts against the booked number. Impressions are also the denominator planners divide by reach to check whether frequency is climbing too fast within a fixed budget. The common slip is reading a large impression total as proof of a large audience, when a small reach hit repeatedly can produce the same number.
The common mistake
Treating impressions as audience size is the common error; impressions measure exposure volume, reach measures unique people.