Cost per acquisition (CPA)

Cost per acquisition is the average media spend required to produce one conversion, calculated as CPA = ad spend / number of conversions. "Acquisition" is deliberately broad: depending on the campaign, it can mean a purchase, a form fill, a free-trial signup, or an app install, so the same acronym can mean different things across teams unless the conversion event is stated explicitly.

CPA is closely related to but not identical to customer acquisition cost: CPA usually measures a single channel's paid media efficiency for one conversion type, while customer acquisition cost is typically the fully loaded cost, including creative, tooling, and headcount, of acquiring an actual paying customer across all channels. It also differs from cost per click and cost per mille, which price the input (a click or an impression) rather than the outcome.

Advertisers set target CPAs to bid automated campaigns and to compare channels on a common basis, but a low CPA is only meaningful next to the value of what was acquired; a cheap lead that never buys is worse than a costlier one that does. Comparing CPA across campaigns with different attribution windows or definitions of conversion is a common source of misleading conclusions.