The AMA defines reach as “the number of different persons or households exposed to a particular advertising media vehicle or a media schedule during a specified period of time. It is also called cumulative audience, cumulative reach, net audience, net reach, net unduplicated audience, or unduplicated audience. Reach is often presented as a percentage of the total number of persons in a specified audience or target market.” 
Reach measures the breadth of an advertisement’s spread across a population. Net reach and frequency are important concepts in describing an advertising campaign; they separate total impressions into the number of people reached and the average frequency with which those individuals are exposed to advertising. A campaign with high net reach and low frequency runs the danger of being lost in a noisy environment. A campaign with low net reach but high frequency can overexpose some audiences and miss others entirely. Reach and frequency metrics help managers adjust their advertising media plans to fit their marketing strategies.
Reach, whether described as “net reach” or simply “reach,” refers to the unduplicated audience of individuals who have been exposed at least once to the advertising in question. Reach can be expressed as either the number of individuals or the percentage of the population that has seen the advertisement.
Reach: The number of people or percent of population exposed to an advertisement.
Net reach: This term is used to emphasize the fact that the reach of multiple advertising placements is not calculated through the gross addition of all individuals reached by each of those placements.
Impressions (#) = Reach (#) x Frequency (#)
MASB on YouTube: Reach vs. Impressions (Kyriakopolous 2020)
- ^ Farris, Paul W.; Neil T. Bendle; Phillip E. Pfeifer; and David J. Reibstein (2010). Marketing Metrics: The Definitive Guide to Measuring Marketing Performance (Second Edition). Upper Saddle River, New Jersey: Pearson Education, Inc.
- ^ American Marketing Association, AMA Dictionary.