Reach and frequency
Reach and frequency are paired media metrics: reach is the number of unique people who saw an ad at least once, and frequency is the average number of times each reached person saw it. Together they decompose total impressions, since impressions equal reach times frequency. Platforms expose both in reach-and-frequency reporting and let advertisers set frequency caps to limit how often one person is shown the same ad.
What this means
Reach counts the distinct people exposed to an ad at least once in a period. Frequency is the average exposures per reached person. Because every impression is one person seeing the ad once, total impressions = reach × frequency — the two metrics partition the same impression total in different ways.
Why frequency caps exist
Beyond a point, showing the same person an ad repeatedly yields diminishing returns and can cause ad fatigue or annoyance. Platforms let advertisers set a frequency cap to bound exposures per person over a window, trading some repetition for broader reach. Choosing a cap is a planning decision, not a benchmark a tool can supply.
- Reach = unique people exposed at least once
- Frequency = average exposures per reached person
- Impressions = reach × frequency; caps bound repetition
Why they mislead
De-duplicating reach across devices and platforms is hard, so cross-channel reach is often estimated, not exact. Frequency is an average that hides the distribution — a few heavily exposed people can pull it up while most see the ad once. Read both with the impression total, not in isolation.
How it appears in analytics and logs
High impressions with low reach and high frequency means a small audience saw the ad many times — useful for recall but risking fatigue; high reach with low frequency means broad but shallow exposure.
Diagnostic use case
Use reach to size unique exposure and frequency to manage repetition, since the same impression total can mean broad-and-shallow reach or narrow-and-repetitive frequency.
What WebmasterID can help detect
WebmasterID measures first-party on-site behaviour, so platform reach-and-frequency figures can be checked against what reached audiences actually did on your site.
Common mistakes
- Reading impressions without splitting them into reach and frequency.
- Treating average frequency as if everyone saw the ad that many times.
- Assuming cross-platform reach is exactly de-duplicated.
Privacy and accuracy notes
Reach and frequency are reported as aggregate audience counts, not individual exposure logs. This page is educational, not legal advice, and endorses no fingerprinting.
Related pages
- Impressions and the viewability problem
An impression counts a piece of content being shown — a search result, an ad, a social post. The trap is that 'shown' has no single definition: Search Console counts a listing appearing in results, ad servers count an ad being delivered, and the IAB/MRC viewable-impression standard requires a portion of pixels visible for a minimum time before it counts. Impressions are only comparable within one definition.
- Share of search
Share of search is the volume of searches for one brand divided by the total search volume for all brands in its category, as a percentage. Computed from search-volume tools or Google Trends-style indices, it is used as a leading, attribution-free indicator of relative brand demand. It measures interest expressed as queries, not sales, so it complements rather than substitutes for share-of-market figures.
- Cost per mille (CPM)
Cost per mille (CPM) is the cost of one thousand impressions — 'mille' is Latin for thousand. It is the standard pricing unit for awareness and display buying, where advertisers pay for exposure rather than clicks. CPM depends entirely on how an impression is defined (served vs viewable), and it says nothing about whether anyone clicked or converted, so it is an exposure-cost metric only.
- Attribution analytics
Connect exposure to first-party outcomes.
Sources and verification notes
- IAB / MRC — Audience reach measurement guidelinesReach/frequency definitions; specific caps are planning conventions.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.