Reach and frequency

Reach is the count of unique people exposed to a campaign at least once; frequency is the average number of times each of those people was exposed, calculated roughly as frequency = total impressions / reach. Together they describe how a fixed number of impressions was distributed: spread thinly across a large audience, or concentrated on a smaller one repeatedly.

The two metrics trade off against each other for a fixed budget: raising reach by targeting more people lowers average frequency, and vice versa. This differs from cost per mille, which prices impressions but says nothing about distribution, and from the related broadcast-media metric Gross Rating Point, which multiplies reach and frequency together into a single number. frequency capping is the practical control advertisers use to keep frequency from climbing too high for any one person.

Reach and frequency matter because both under- and over-exposure hurt a campaign: too little frequency and an ad never registers; too much and it risks ad fatigue, wasted spend, and in some cases actively annoying the audience, which shows up in falling brand lift or engagement over the course of a flight. Planners set target reach and frequency ranges before a campaign runs, then measure delivered impressions against them.