Cost per thousand in a store network
Cost per thousand is the standard unit for comparing media cost, and in a store network it rests on an estimate rather than a count. The plays are measured; the audience per play is modelled, and the model is where the number comes from.
Understanding the construction is what makes a CPM comparable to anything.
How is the figure built?
Spend divided by estimated impressions, where impressions are plays multiplied by an estimated audience per play. The plays half is verifiable from playout logs; the audience half is an estimate.
A network that reports both halves separately is being transparent about which part is measured.
What drives the audience estimate?
Store traffic, the proportion of that traffic passing the screen position, and an assumption about opportunity to see. Each of those can be estimated well or badly, and small changes in the assumptions move the CPM substantially.
Ask what the opportunity-to-see definition is. A generous definition inflates impressions and deflates the CPM without anything changing in the store.
What is the honest comparison?
Against other estimates built the same way, which in practice means within the same measurement framework. Cost per mille as a concept is universal; the audience definitions behind it are not.
Comparing an in-store CPM against a digital CPM compares two different definitions of an impression, and the comparison usually flatters whichever has the looser definition.
Why is a screen impression not a digital impression?
Because a digital impression is a served ad on a device with a rendered opportunity, and a physical impression is a person in proximity to a screen that played. Neither is necessarily seen, and they are unequal in what they represent.
Anyone comparing them without stating the definitions is making a comparison that cannot be interrogated.
What should be checked about a CPM?
The audience definition, whether impressions are delivered or planned, whether uptime is accounted for, and what population the audience estimate is drawn from. Four checks, each capable of moving the number.
Delivered rather than planned is the critical one. A CPM computed on planned delivery describes the invoice rather than the campaign.
Is CPM the right buying metric here?
It is a comparison unit and it is a poor sole objective, because it measures cost per opportunity rather than cost per outcome. Where an outcome can be measured — and in this channel it frequently can — cost per outcome is the stronger basis.
What should appear in a proposal?
Plays, audience estimate with method, resulting impressions, spend and CPM. Five figures, and the chain between them should be visible.
Frequently asked questions
Is a low CPM good?
Only against a comparable definition. A low CPM built on a generous audience assumption is cheaper arithmetic rather than cheaper media, which is why the definition matters more than the number.
Can impressions be verified?
Plays can, from playout logs. The audience per play cannot be verified without independent measurement, which is why the two halves should be reported separately.
How does uptime affect CPM?
A screen that was dark delivered no impressions, so a CPM computed without accounting for uptime understates the real cost. Ask whether the figure uses delivered or scheduled plays.
Should I compare in-store CPM to television?
With considerable caution and the definitions stated. The measurement frameworks differ enough that a direct comparison is closer to a category error than an insight.
What about cost per store per day?
It is a useful supplementary unit because it is unambiguous and verifiable. It does not adjust for traffic, which is why it complements rather than replaces a CPM.
Does a premium position justify a higher CPM?
If the audience estimate already reflects the position's traffic, the CPM should capture it. A premium charged on top of an audience-adjusted CPM is a pricing decision rather than a measurement one.
How often should the audience estimate be refreshed?
Regularly, because store traffic changes. An estimate built two years ago describes a different estate.
Is there a standard for this channel?
Out-of-home measurement standards exist and adoption varies. Industry practice is developed by bodies such as Geopath, and it is worth asking how closely a network aligns.
What is the single most useful question?
Is this CPM based on delivered plays and what is the opportunity-to-see definition. The answer tells you what the number means.
### What should sit alongside a CPM in a proposal?
Cost per store per day and cost per delivered play. Both are unambiguous and verifiable, and together they let a buyer sanity-check a CPM built on an audience estimate.
Where the three figures do not reconcile, the audience assumption is doing more work than it should, and that is the conversation to have before the buy.
Does a premium position deserve a premium price?
If the audience estimate already reflects it, the CPM captures it and a further premium is a pricing decision. Stating which of the two is happening keeps the negotiation honest.
### How should CPM be used across a programme?
As a tracking metric over time within the network, where the definition is constant and movements are meaningful. Its weakness is cross-channel comparison rather than internal consistency.
Tracking it alongside cost per store per day shows whether a change came from pricing or from the audience estimate being revised, which are different things.
What if the audience method changes?
The series breaks, and the change should be announced with a restated history. A CPM series spanning a methodology change is two series presented as one.
Is CPM a good negotiation basis?
It is a familiar one and it embeds an estimate. Negotiating on cost per store per day and delivered plays is more concrete and harder to move by assumption.
Considering NRS Digital Media? Start at nrsdigitalmedia.com, read the media deck, or contact the team.