CPA (Cost Per Action or Cost Per Acquisition) is an advertising pricing model in which the advertiser pays for a specific action taken by the user — a purchase, a form submission, an account registration. Unlike CPC or CPM, CPA directly links the cost of advertising to its business result.
Definition and formula
CPA = total campaign cost / number of conversions
Example: a campaign cost PLN 1,000 and generated 50 contact-form submissions. The CPA is PLN 20.
CPA as a metric and as a pricing model
CPA is used in two senses — worth distinguishing:
CPA as a metric — we calculate it ourselves by dividing spend by the number of conversions. It can be calculated for any campaign, regardless of whether we’re billed by the platform on a CPC, CPM, or other basis.
CPA as a pricing/optimization model — in Google Ads, Meta Ads, and other systems you can set up a campaign so the algorithm automatically optimizes toward a target CPA. The advertiser specifies the maximum they want to pay per conversion, and the platform tries to deliver conversions at that cost.
Where is CPA used?
- Google Ads — the “Target CPA” strategy automatically optimizes bids toward a set cost per conversion
- Meta Ads — conversion optimization with a CPA goal
- Affiliate networks — the CPA model is the basis of affiliate marketing, where the publisher earns a commission for each conversion generated
What determines the CPA?
CPA is the product of two factors: the cost per click (CPC) and the conversion rate (CR).
CPA = CPC / conversion rate
If a click costs PLN 2 and 5% of visitors convert, the CPA is PLN 40. To lower CPA, we can either lower CPC (e.g. by improving ad quality) or raise the conversion rate (e.g. by improving the landing page).
A good CPA — how to judge it?
CPA on its own doesn’t tell you whether a campaign is profitable. PLN 50 per conversion can be a great result when selling a PLN 500 product, and a terrible one for a PLN 60 product. That’s why CPA should always be assessed in the context of the conversion’s value — hence the importance of ROAS and ROI.
Summary
CPA is the cost of acquiring one conversion. It’s one of the most important performance metrics, because it directly links ad spend to the business result. To lower it — improve ad quality or the landing page. To judge it — always compare it with the value that the conversion generates.
