Reach counts the distinct people or accounts exposed to content within a reporting scope. Impressions count the number of recorded exposures. One person can contribute several impressions while counting once toward reach in that scope.
The exact measurement depends on the platform. Exposure also does not prove someone paid attention, remembered the message, or bought the product.
A simple example
Suppose an ad is shown to Alex three times, Sam twice, and Jo once.
- Reach: 3 people.
- Impressions: 6.
- Average frequency: 2 impressions per reached person.
The average hides the distribution. Alex saw the ad more often than Jo did.
In real reports, reach may be estimated or modeled rather than a direct count of identifiable individuals. Google’s reach measurement documentation explains this for its advertising reporting.
Why reach cannot simply be added
Imagine a post reaches 1,000 accounts on Monday and another reaches 1,200 on Tuesday. If 500 accounts are in both groups, the combined reach is 1,700, not 2,200.
Adding the two figures counts overlapping accounts twice. The same issue applies to multiple ads, campaigns, or reporting periods.
Use a report that calculates reach across the combined scope when it is available. If you add separate reach values, label the result as a sum of reported reach rather than unique people.
Cross-platform reach has the same problem
A person may use Instagram, YouTube, and another service. Adding the reach reported by each does not tell you how many different people you reached overall.
Without a suitable deduplicated measurement method, report the platforms separately. Do not present the sum as a verified unique audience.
This matters when comparing a single-platform plan with a multi-platform plan. The same budget can buy a different mix of new exposure and repeated exposure.
How frequency connects the measures
Within matching definitions and dates:
Average frequency = impressions ÷ reach.
If impressions rise while reach changes little, the campaign may be delivering more repeated exposure to roughly the same audience. That may be appropriate for a reminder, or it may prompt a review of audience size and response.
See the ad frequency guide before treating a particular average as evidence of fatigue.
Which metric should you use?
Reach helps describe the breadth of exposure. Impressions help describe delivery volume and support calculations such as CPM.
Neither measures a business result on its own. Pair exposure with metrics suited to the objective, such as qualified enquiries, sales, or a properly designed awareness study.
For cost calculations, the CPM calculator uses impressions, not reach. Substituting reach creates a different cost measure and should be labeled accordingly.
A reporting checklist
Include the platform, date range, content scope, and whether the metric represents people or accounts. Explain any estimation, unavailable data, or overlap you cannot remove.
Finally, ask whether the comparison uses the same definitions. A clear explanation of a smaller number is more useful than an impressive total that counts the same audience repeatedly.