CPM, CPC, CPA: which metric to buy on
CPM charges per thousand impressions, CPC per click, and CPA per completed action. The difference is who carries the risk. On CPM the advertiser carries it, on CPA the publisher or platform does, and the price rises as risk shifts away from you.
Choosing a pricing model is not really a pricing decision. It is a decision about which part of the funnel you are confident in, and pricing follows from that.
CPM, cost per mille
You pay per thousand impressions served, regardless of what follows. All performance risk sits with you: if the creative fails or the audience is wrong, you still pay in full.
It is the right model when the objective genuinely is exposure, such as brand campaigns or account based programs where you are trying to be present with a defined set of companies rather than drive immediate clicks. It is also the most transparent model, because impressions are the easiest unit to verify independently.
CPC, cost per click
You pay only when someone clicks. The platform absorbs the risk of serving impressions that go nowhere, and prices accordingly.
The failure mode is that a click is not an outcome. Optimising towards CPC pushes delivery towards audiences that click habitually, which is not the same as audiences that buy. In B2B, cheap clicks from unqualified traffic are a common and expensive trap.
CPA, cost per action
You pay on a defined action: a form completion, a signup, a qualified lead. Most risk sits with the seller, so the unit price is highest.
Two cautions. The action definition is everything, and loose definitions get exploited. And CPA inventory tends to be narrower, since platforms only accept the risk where they are confident, which limits scale.
Choosing between them
- Buy CPM when you are confident in the audience definition and the objective is presence rather than immediate response.
- Buy CPC when the landing experience converts reliably and you want traffic volume, with qualification filters applied downstream.
- Buy CPA when the action is tightly defined, you can verify quality, and you are willing to trade scale for reduced risk.
The metric that actually matters
All three are input costs, not outcomes. The number that decides whether a campaign worked is cost per qualified opportunity, and it is the one most reporting quietly avoids because it requires connecting media data to CRM data.
A campaign with an unattractive CPM producing pipeline beats an efficient CPC producing traffic that never qualifies. If your reporting stops at platform metrics, you are optimising the input and guessing at the result. That connection is usually the first thing our consulting engagements rebuild.
A note on comparing quotes
CPMs are only comparable when the underlying impression is comparable. A viewable, verified, brand safe impression on a private marketplace is a different product to an open auction impression, even at the same nominal CPM. Compare on the same Media Rating Council viewability basis or you are comparing nothing.
Common questions
CPM has the lowest nominal unit price and the highest risk. CPA has the highest unit price and the lowest risk. Neither is cheaper once you account for what fails to convert, which is why cost per qualified opportunity is the honest comparison.
Yes, and most mature programs do. Upper funnel on CPM for presence, lower funnel on CPC or CPA for response, with reporting rolled up to a single cost per opportunity.
Because the impressions are not equivalent. Inventory quality, viewability standard, audience targeting, and fee chain all move the number. See how programmatic buying works.
Work out which model fits your objective
Tell us the campaign objective and current channel mix. We will model the pricing approach that matches it, and what pooled rates would do to the numbers.