Reach

Reach is the number of different people who saw your campaign at least once over a given period. Each person counts once, however many times they passed the screen.

How is it measured?

Reach starts from impressions, then removes the repeats. If the same commuter walks past your screen every morning for two weeks, that is a lot of impressions but only one person reached.

On digital out-of-home (DOOH) screens, in streets, malls and stations, nobody logs in, so nobody can count unique people directly. Reach is modelled instead: audience institutes and measurement tools combine traffic counts with mobility data to estimate how often the same people come back to the same places. The result is always an estimate, and it should always state the period it covers.

Reach and frequency are two sides of the same budget. Divide impressions by reach and you get the average frequency: how many times each person saw your ad.

Example

Illustrative example: your campaign runs for one week and delivers 50,000 impressions. The measurement estimates that 10,000 different people saw it. Your reach is 10,000 people, and the average frequency is 5. Spread the same budget over more screens in more places and you might reach 20,000 people, but each of them would see the ad only 2 or 3 times.

Why it matters when you plan a DOOH campaign

Reach is tempting to maximize: a bigger number looks good in a report. But reach spread thin across a whole city mostly means many people saw your ad once, then forgot it.

For a local business, the reach that counts is the people who live, work or shop near you. A campaign concentrated on the screens around your door reaches fewer people in total, but more of the right ones, and often enough for them to remember you.

So always read reach next to frequency, and next to place. Ask three questions: reached where, over how long, and how many times each?