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Metrics
CPA
The average cost to generate one conversion, whether that's a purchase, signup, lead, or other defined action. Calculated as total ad spend divided by total conversions. The core efficiency metric for performance marketing. Important to distinguish between platform-reported CPA (based on attributed conversions, often inflated) and true incremental CPA (based on conversions your ads actually caused). A 'low' CPA that's based on overclaimed conversions is actually a mirage.
Why it matters
It is the cost side of the equation with no revenue in it, which makes it useful for comparing efficiency and dangerous for judging value.
In practice
Never optimise CPA alone. A falling CPA alongside a falling AOV is usually a worse business, not a better one.
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