CPM, cost per mille, is the price of one thousand ad impressions.
Definition
CPM, cost per mille, is the price of one thousand ad impressions. It is the standard pricing and comparison unit for awareness and reach buying, and it is also the currency of most programmatic and display auctions even when the buyer is optimising toward clicks or conversions — the platform converts the buyer's goal into an effective bid per thousand impressions to compete in the auction.
CPM by itself says nothing about results; it is an input cost. What matters is the cost per outcome it produces, which depends on the click-through rate and conversion rate of the traffic that the CPM buys.
A $2 CPM with a 0.1% CTR delivers clicks at $2 each; a $5 CPM with a 0.5% CTR delivers clicks at $1 each, so the more expensive impressions are the cheaper clicks. Buyers therefore read CPM alongside downstream rates rather than chasing the lowest CPM.
In context
For iGaming media buyers, CPM varies by source, format, GEO, targeting tightness and competition. Tier-1 regulated markets command far higher CPMs than Tier-3 markets; narrow targeting raises CPM because fewer impressions match; and gambling-permitted inventory is scarcer and therefore pricier than open inventory.
A rising CPM over a campaign's life is a normal saturation signal — as the campaign scales, it wins impressions from a less-responsive pool at a higher clearing price.
CPM also interacts with creative quality on auction-based platforms. A strong creative earns a higher predicted engagement score, so the platform charges a lower effective CPM to serve it — the same bid wins more impressions at less cost.
This is why creative testing improves not just CTR but the whole cost structure of a campaign, and why a fatigued creative shows up as a rising effective CPM before it shows up as a falling conversion rate.
Worked example
A buyer's push campaign runs at a $1.10 CPM with a 0.35% CTR, delivering clicks near $0.31. A new creative lifts CTR to 0.55% at the same $1.10 CPM, dropping click cost to $0.20 and, with conversion rate holding, cutting cost per FTD by roughly a third.
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