Basics · also called unique reach
Reach
Reach is the number (or percentage) of unique people or households who saw an ad at least once during a campaign, as opposed to the total number of impressions.
Reach counts heads, not showings. If a campaign delivers 10 million impressions to 2.5 million different people, its reach is 2.5 million, and the average frequency is 4. It is often expressed as a percentage of a target audience ("we reached 40% of adults 18–34 in Mexico").
Reach is the classic metric of TV and brand advertising, where the goal is making many people aware. It pairs with frequency in reach and frequency planning and underpins gross rating points.
Measuring unique reach across channels is hard. Each platform de-duplicates only within its own walls, so adding up reach from YouTube, Meta and a CTV app double-counts people. Cookies and device IDs also inflate reach when one person uses several devices or clears cookies. Industry efforts to measure cross-media reach, such as the ANA's Aquila program in the US, exist precisely because of this.
Think of it like this
Reach is the number of different guests who came to your party; impressions are the total number of times the door opened.
An example
A campaign in Brazil serves 30 million impressions at an average frequency of 3, so reach is about 10 million people.
Related terms
Reach and frequency
Reach and frequency are paired metrics: reach is how many different people saw an ad, and frequency is the average number of times each of those people saw it.
Frequency capping
Frequency capping is a setting that limits how many times the same person, device or household sees a particular ad within a set period, such as three times per day.
Gross rating point (GRP)
A gross rating point (GRP) measures advertising weight: reach as a percentage of a target population multiplied by average frequency, so 1 GRP equals impressions equal to 1% of that population.
Impression
An impression is one instance of an ad being served and counted as displayed to a user; it is the basic unit that most online advertising is bought and sold by.
Campaign
A campaign is an organised set of ads with a shared goal, budget, audience and time period, run across one or more channels and measured against defined KPIs.