CPM (Cost Per Mille) is the oldest and simplest ad-pricing model: an advertiser pays a set amount for every 1,000 impressions, whether or not anyone clicks or converts. "Mille" is Latin for thousand. Because it charges purely for exposure, CPM is the default way to buy and sell brand and awareness inventory.

How to calculate CPM

CPM = (Campaign cost / Impressions) x 1,000

CPM = (Campaign cost / Impressions) x 1,000

CPM = (Campaign cost / Impressions) x 1,000

Multiplying by 1,000 is what puts the price on a per-thousand basis, which is the unit advertisers have used for decades to compare exposure across very different placements.

A quick example

A campaign that costs $500 and generates 100,000 impressions has a CPM of $5.

That $5 buys 1,000 chances to be seen. Whether those chances are worth it depends entirely on who sees the ad and what they do next, which is exactly what CPM does not tell you.

What counts as a good CPM?

For an advertiser, a good CPM is a low one for the audience they want. For a publisher, the goal is the opposite: a high effective rate for the inventory they sell. Actual CPMs swing with geography, format, and season. A rewarded video slot in a high-spending market can command many times the CPM of a banner in a low-spending one, so a single benchmark rarely means much.

CPM vs. eCPM

CPM is what an advertiser pays; eCPM is what a publisher effectively earns per 1,000 impressions across any pricing model. Publishers use eCPM to compare how well different ad units perform. The difference matters most when a placement is not sold on a straight impression basis: a rewarded or offer-based unit priced on completed actions still has an eCPM, even though no advertiser ever quoted it a CPM.

How publishers lift effective CPM

• Add competing demand. More buyers bidding on each impression raises the clearing price.

• Mix in higher-value formats. Rewarded video and an offerwall earn far more per impression than standard banners.

• Improve audience quality. Engaged users in strong markets draw higher bids.

Why offerwalls often win on eCPM

Because an offerwall is paid on completed offers by motivated users rather than on passive views, its effective earnings per thousand impressions typically run well above standard banner or interstitial CPMs. One user finishing a valuable offer can outproduce thousands of impressions sold on a flat CPM, which is why publishers layer offerwalls on top of their impression-based inventory rather than replacing it.

Common mistakes to avoid

• Treating CPM as a revenue metric. It is a price for exposure, not a measure of outcomes.

• Comparing CPMs across geographies as if a dollar of exposure were worth the same everywhere.

• Chasing CPM while ignoring fill. A high CPM that rarely fills earns less than a modest CPM that always does.