What is CPA?
CPA (Cost per Acquisition) is the average advertising cost required to generate one Conversion—for example, a purchase, signup, or subscription start. It’s a core efficiency metric used across paid channels to evaluate whether a Campaign is profitable and scalable. Unlike CPC or CPM, CPA looks past clicks and impressions to the bottom-line action.
What is CPA? In plain terms: how much you pay, on average, for one desired outcome.
How to calculate CPA
Formula:
CPA = Total Ad Spend ÷ Number of Conversions
Example: Spend €1,200 and record 60 conversions → CPA = €20.
Pair CPA with Conversion Rate and CTR to diagnose funnel issues: high CPC + low conversion rate typically inflates CPA.
CPA vs. CPL and ROI
- CPL counts leads, not final actions. If only 25% of leads buy, your effective CPA is CPL ÷ 0.25.
- CPA connects directly to unit economics. Compare CPA to LTV and AOV to judge payback and ROI.
Tracking across analytics tools
CPA isn’t a native metric; it’s derived by combining ad spend with conversion counts in platforms like GA4 as well as privacy-friendly alternatives such as Plausible or Matomo, or via server-side pipelines into BigQuery and dashboards in Power BI. Reliable CPA requires:
- Clean conversion definitions (avoid counting Micro-Conversion as primary goals).
- Consistent UTM tagging to attribute spend to the correct Source/Referral/Organic Search buckets.
- Thoughtful Attribution/Attribution Model selection; last-click vs. data-driven can materially change CPA.
Optimization checklist
- Improve on-site UX to lift conversion rate (Session quality and Engaged Sessions).
- Prune expensive audiences/keywords; bid to a target CPA where supported.
- Tighten creative and landing-page message match.
- De-duplicate tracking via Tag Management to avoid inflated conversion counts.
When to use CPA
Use CPA for performance channels where the action value is stable (e.g., fixed-price products or standard lead-to-sale rates). For variable value per conversion, monitor revenue-based metrics alongside CPA.