SYS/DEF
CPA
Cost per acquisition: campaign spend divided by the conversions that campaign is credited with.
Definition
CPA is media spend (and sometimes platform fees) divided by conversions attributed to the campaign. If you spend €3,000 for 50 demo requests, CPA is €60. It is a campaign ratio, not the firm’s full economics — that is CAC.
CPL (cost per lead) is a CPA whose conversion is a lead. Naming it clearly stops you comparing a form CPL to a purchase CPA.
When it matters
Daily SEA steering, briefing a landing test (a better CVR should lower CPA at constant bids, otherwise the traffic is not the same), and computing post-acquisition margin.
Paired with ROAS, it says whether the euro spent comes back. Alone, it can hide a cheap conversion with no value.
Pitfalls
Comparing CPAs on different conversions (lead vs sale). Changing the attribution window and celebrating a “drop”. Forgetting VAT, Ads A/B tests that split budget, or double-imported conversions. Treating the platform’s target CPA as a law of physics rather than a bid lever.
Related terms
Related tool
The three numbers that get confused once per meeting: Open CPA and ROAS.