CPA (Cost Per Acquisition) is the average cost in ad spend required to drive one conversion — typically a purchase, signup, or qualified lead — calculated as total spend divided by total conversions.
CPA is the unit-economics counterpart to ROAS. Where ROAS expresses ad efficiency as a revenue ratio, CPA expresses it as an absolute cost: how much you paid in ads to drive one conversion. Calculated as total ad spend divided by total conversions over the same window. A campaign spending $10,000 driving 200 conversions has $50 CPA.
The conversion event being counted matters. 'Purchase CPA' counts revenue-generating purchases; 'Lead CPA' counts form submissions or qualified leads; 'Signup CPA' counts account creations for SaaS. Each network's reporting uses the conversion events you've configured on its tracking layer (Meta Pixel events, Google conversion actions, LinkedIn Insight Tag conversions).
Per-platform CPA is what each network reports natively. As with ROAS, it suffers attribution overlap — multiple platforms can each claim credit for the same conversion. Blended CPA — total ad spend across all platforms divided by total unique conversions — is the unbiased portfolio metric. Tools like Gapscout compute it by aggregating both halves via Marketing APIs.
CPA targets vary dramatically by buyer LTV. A SaaS company with $5,000 LTV can afford $500 CPA and still be 10x profitable; a low-margin ecommerce SKU with $40 average order value needs CPA under $15 to work. The reference ratio is LTV:CAC — most healthy SaaS targets 3:1 or higher; healthy ecommerce targets 3:1+ within a payback window of 90 days.
Gapscout's reporting surfaces CPA per-platform and blended across all six supported networks. The audit agents include CPA-regression checks — campaigns whose CPA has worsened against their own 30-day baseline get flagged with the recommended action (typically pause-and-investigate or budget-cut).
ROAS (Return on Ad Spend) is the ratio of revenue generated by an ad campaign to the spend on that campaign — typically expressed …
LTV:CAC ratio compares the lifetime value of an acquired customer to the cost of acquiring them — a 3:1 ratio (LTV three times CAC…
CTR (Click-Through Rate) is the ratio of users who clicked an ad to users who saw it — calculated as clicks divided by impressions…