Cost per Acquisition (CPA)
Advertising spend divided by the number of tracked acquisitions or actions.
Cost per acquisition measures how much a campaign spends to produce a defined conversion. Teams also use CPA to mean cost per action, so document whether the acquisition means a lead, trial, or paying customer. A platform’s conversion setting determines what its reported CPA actually represents.
Example: A SaaS campaign spends $1,200 and records 40 trial starts, giving a trial CPA of $30. If eight trials later become paid accounts, campaign spend per paid acquisition is $150. Both figures are useful, but they answer different questions about the funnel.
Watch out: CPA is not automatically the same as fully loaded customer acquisition cost. A paid-media report often excludes salaries, agency work, sales effort, and organic acquisition costs. Attribution windows also affect the reported result: a purchase outside the tracking window might be missed. Compare campaigns using the same event and follow the cohort through retention before judging whether an inexpensive acquisition creates durable value.
Further reading: Ahrefs: marketing metrics.
Related: cost per lead, conversion rate.