CPA, cost per action or acquisition, is total spend divided by the number of completed actions it drove. Unlike CPC or CPM, it prices the outcome you actually care about, which makes it the bottom-line efficiency metric for performance campaigns.
Why it matters for agencies
CPA is the product of upstream metrics: CPA = CPC ÷ conversion rate. You can lower it by cutting click costs or by lifting conversion — and the latter is usually cheaper. A target CPA should be set from unit economics (margin and LTV), not chosen arbitrarily.
Run the numbers with the free CPA calculator.