CPA (Cost Per Acquisition)
Cost Per Acquisition is the average ad spend per conversion event, typically counted within an ad platform. CPA is what ad platforms show; CAC is what your finance team sees.
CPA is the metric ad platforms (Meta, Google, LinkedIn) report: total ad spend / reported conversions. If you spent $1,000 and Meta reported 50 purchases, CPA is $20.
CPA is always a platform-defined, within-platform number. It counts conversions the platform takes credit for — which means it includes view-through conversions (Meta), click-through conversions (Google), and cross-device attribution the platform assigns to itself.
CAC (Customer Acquisition Cost) is the finance-grade equivalent: blended acquisition spend across every channel and function, divided by new customers. CAC > CPA almost always, because CAC includes non-ad costs (salary, tooling, agency fees) and doesn't double-count conversions across platforms the way stacked CPAs do.
Target CPA bidding is a Google Ads feature that optimizes against a CPA goal. It works best when you have 30+ conversions per month in the ad account — below that, the algorithm does not have enough signal to optimize stably.