Impression multiplier

The impression multiplier is the average number of people who have a chance to see a single ad play on a digital out-of-home (DOOH) screen, in a street, mall or station. It turns plays into impressions.

How does it work?

Online, one impression usually means one person looking at one device. A public screen works differently: when your ad plays, everyone in front of the screen at that moment can see it. That is collective exposure, and the multiplier puts a number on it.

The multiplier is not fixed. It changes with the place and the hour. A station hall at rush hour gives a high multiplier. A quiet corridor late at night can drop below one, because some plays happen with nobody around.

How is it estimated?

Nobody clicks a screen, so the multiplier is always an estimate:

• Direct counts on small networks: footfall counters, till receipts, badge scans.
• Sensors: Wi-Fi or Bluetooth detection, anonymized cameras, motion sensors.
• Audience institutes such as CIM in Belgium or ROUTE in the UK, which model audiences from traffic data, screen size, viewing distance and travel speed.

Some figures go one step further and correct each contact for real visibility, which is what a VAC does.

Example

Illustrative example: a screen plays your ad 100 times in a day, for €50 in total. In a mall where each play reaches around 10 people, that is 1,000 impressions and a CPM of €50. On a quiet screen where each play reaches around 2 people, the same €50 buys 200 impressions, and the CPM becomes €250.

Why it matters when you plan a DOOH campaign

A price per play tells you little until you know the multiplier behind it. Two offers at the same cost can deliver very different audiences. Before you compare a CPM, ask how the impressions were counted, and by whom.

It also keeps the conversation honest. A street screen is one-to-many: it speaks to everyone nearby, not to one profiled person. The multiplier is how you count that crowd without pretending each viewer was targeted. Plan on the places where the multiplier is high for the people you want, at the hours when they are actually there.