Glossary
Reach or impressions: the difference that changes the report
Reach counts people, impressions count deliveries. How dividing one by the other gives frequency, and why swapping them inflates every report you send.
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Reach counts people. Impressions count deliveries. Swapping the two is the most common substitution in paid media reporting, and it always inflates the apparent result, because impressions is the bigger number.
The difference in one line
- Reach: how many different people saw the ad at least once.
- Impressions: how many times the ad was delivered, including repeats.
An ad with 40,000 impressions and 10,000 reach was seen by ten thousand people, four times each on average. Anyone reporting "we reached 40 thousand people" is reporting a number four times the truth.
The metric born from the division
Frequency = impressions ÷ reach.
This is where the two numbers become a decision. Frequency warns that the audience is saturating, usually before cost per result rises.
| Frequency in the period | Usual reading |
|---|---|
| Near 1 | Large audience, little repetition |
| Between 2 and 4 | Common range for a running campaign |
| Above 5 | High repetition; check cost and creative |
The thresholds move with objective and audience size, so treat the table as a starting point, not a rule. The detail is in frequency.
When to use each
Use reach when the question is coverage: how many of the audience were touched, how much of the available audience is left. It is the top-of-funnel and launch metric.
Use impressions when the question is exposure or media cost. CPM is calculated on impressions, not reach, and comparing CPM across campaigns only makes sense on that basis.
Use both together when the question is saturation. Flat reach with rising impressions means budget is buying repetition to the same people.
The mistake of adding across periods
Reach does not add. January's reach plus February's is not the bimonthly reach, because the same people show up in both months. Impressions add, reach does not.
That is why every report has to state the reach period. Changing the date range moves the number without anything happening in the campaign, and it is one of the reasons two reports from the same account never agree. The individual definitions are in reach and impressions.
The report template that states the period and avoids the bad sum is on the paid media reporting page.
Frequently asked questions
What is the difference between reach and impressions?
Reach is the number of different people who saw the ad at least once. Impressions is the number of times it was delivered, counting repeats to the same person.
Are impressions always higher than reach?
Yes, or equal. Since every person reached generates at least one impression, impressions can never be lower than reach. Dividing one by the other gives frequency.
Which one should go in the report?
Both, and never one in place of the other. Reach answers how many people were touched; impressions answers how many times; and frequency, which comes from the division, warns when the audience is saturating.