CPA vs CAC: the difference and why it matters for ecommerce
CPA and CAC sound similar but measure different things. Confusing them leads to underestimating what it really costs to acquire a customer — and overestimating campaign profitability.
Calculate my CPAThe core difference
CPA
Ad Spend ÷ Sales
Cost of acquiring a customer through a specific campaign or channel. Only includes ad spend.
CAC
Total Marketing Costs ÷ New Customers
All costs to acquire a customer: ads + team + tools + content + agency fees + all other marketing expenses.
CPA is always ≤ CAC. CPA only counts ad spend. CAC adds everything else — salaries, software, creative production, influencer fees, email platform costs, etc.
When to use CPA vs. CAC
Use for campaign-level decisions: is this ad set profitable? Should I pause this audience? This campaign performs vs. others? CPA is tactical — it lives in the ad manager.
Use for business-level decisions: is our marketing sustainable? Are we growing profitably? Can we justify hiring another marketer? CAC is strategic — it lives in the P&L.
LTV:CAC ratio
For sustainable businesses, a LTV:CAC ratio of 3:1 or higher is considered healthy — meaning each customer generates 3x what it cost to acquire them over their lifetime.