CPA (Cost per Action/Acquisition)
The average ad cost per conversion event — the core paid efficiency metric.
Cost per Action (CPA) — often used interchangeably with Cost per Acquisition — is the total ad spend divided by the number of completed conversion events (purchase, signup, lead, demo, etc.). CPA is the primary efficiency metric for paid campaigns.
Context
Target CPA varies by business model: a SaaS free-trial signup might be $30; a demo request $200; an enterprise closed-won deal might be $5,000. The 'right' CPA is entirely dependent on unit economics.
Platform-reported CPA suffers the same attribution inflation as platform-reported ROAS — Meta and Google often both take credit for the same conversion. Blended CPA (total spend ÷ total conversions) is more honest.
A B2B SaaS with $3,000 ACV and 15% sales-cycle close rate can afford approximately $450 cost per SQL ($3,000 × 15% ÷ 1.0 LTV:CAC with margin). At $300 SQL CPA, the economics work; at $800, they don't.
CPA improvements from creative or bidding changes often reverse themselves as the account scales. The $50 CPA achieved at $5K/month spend is rarely sustainable at $50K/month; target CPA should be benchmarked at planned scale.
Related terms
Services that apply this
More Paid Media terms
CAC Payback Window
The number of months until a new customer's contribution margin equals the cost to acquire them.
LTV:CAC Ratio
Customer lifetime value divided by customer acquisition cost.
MER (Marketing Efficiency Ratio)
Total revenue divided by total marketing spend — a blended metric that resists attribution gaming.
CPM (Cost per Mille)
Cost per 1,000 impressions — the core pricing unit for paid media.