The metric versus the target
CPA the metric is spend ÷ conversions for whatever you counted as a conversion. Target CPA is the bidding strategy that tells Google to chase that number. The catch is that CPA is only as meaningful as the conversion behind it: a cheap CPA on a shallow event like a form fill can hide an expensive CAC.
CPA versus CAC
People use CPA and CAC loosely, but they are not the same. CPA usually counts a platform conversion (a lead, a signup); CAC is the full cost to win a paying customer. Optimize to a CPA on the wrong event and you can scale cost while starving revenue, which is why we tie CPA back to the qualified end of the funnel.
Common questions
What is the difference between CPA and CAC?
CPA is the cost per platform conversion, which might be a lead or signup. CAC is the total cost to acquire a paying customer. A low CPA on a low-intent event can still produce a high CAC.
Is CPA the same as Target CPA?
No. CPA is the reported metric. Target CPA is a Smart Bidding strategy that aims to hit an average CPA you set; actual CPA will vary around it.