Reach and frequency

Reach is the number of unique people or households exposed to an ad in a period; frequency is the average number of times each saw it, so impressions equal reach times frequency.

The two numbers describe a campaign better than impressions alone. A million impressions can mean 500,000 people seeing the ad twice or 50,000 people seeing it twenty times. Google's open-source Meridian model defines both precisely (Google Meridian documentation, accessed 9 November 2026). Reach counts the unique individuals exposed within each time period, not the running total across periods. Frequency is total impressions divided by reach for that period.

Meridian also notes that many marketing mix models ignore reach and frequency because accurate data is missing for some traditional channels, and it offers a model that uses them where they exist. The average hides the spread: a frequency of four can mean most people saw the ad twice while a small group saw it twenty times. Planners therefore look at the frequency distribution and at reach by frequency level, such as "reach at 3+".

Example: A CTV campaign delivers 2,000,000 impressions to 500,000 households, an average frequency of 4.0. The distribution shows 60,000 households at ten or more exposures. A household-level cap of six would move those impressions to new households and raise reach.

Related terms: frequency capping, MMM, household graph, CTV, incrementality, CPM.

Authoritative source: Google Meridian documentation, "Reach and frequency" (accessed 9 November 2026).