MetricAlso: cost per acquisition, cost per conversion, CAC, customer acquisition cost

CPA (Cost Per Acquisition)

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.

IN GAPSCOUT

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).

Common questions

What's the difference between CPA and CAC?
CPA (Cost Per Acquisition) is commonly used at the campaign or platform level — the cost in ad spend to drive one conversion. CAC (Customer Acquisition Cost) is the business-level metric — total sales + marketing cost to acquire one customer, including non-ad spend. Healthy companies track both.
Should I target a specific CPA?
Yes, but the right target depends on LTV. Calculate your LTV (revenue per customer over their lifetime); your target CPA should be at most LTV / 3 to maintain a 3:1 LTV:CAC ratio. Below that ratio, the business doesn't scale profitably even at high spend volume.
How is CPA different from ROAS?
Inversely related: ROAS = AOV / CPA, where AOV is average order value. A campaign with $80 AOV and $20 CPA has 4x ROAS. CPA is the absolute-cost framing; ROAS is the efficiency-ratio framing. Both matter — high-AOV brands track ROAS, transactional brands often track CPA.