What is CPA?

Cost Per Acquisition

DEFINITION

Cost Per Acquisition (CPA) is the ad spend needed to generate one conversion — a sale, signup, or lead.

FORMULA

CPA = Ad spend ÷ Conversions

BENCHMARKS

Meta ecommerce: $28-$65 · Google Search ecommerce: $35-$80 · B2B lead: $80-$400

Why CPA matters

CPA is cleaner than ROAS for comparing across products with different price points. Used in lead gen where the final sale happens outside the ad platform. Target CPA should always be < LTV × margin × acceptable payback period.

Worked example

Plug a real number into the formula to see CPA in action:

// Formula

CPA = Ad spend ÷ Conversions

// Example calculation

$10,000 spend ÷ 200 conversions = $50 CPA

Numbers are illustrative. Try our Customer LTV Calculator for your real numbers.

Common mistakes with CPA

1
Looking at single-channel ROAS in isolation instead of blended MER. Last-click attribution overweights bottom-funnel channels and starves top-of-funnel.
2
Setting a uniform target across products with different margins. A 2× ROAS is profitable on 80% margin and unprofitable on 20%.
3
Optimizing CAC without measuring LTV. Cheap customers with bad retention destroy unit economics.

How to improve CPA

Run incrementality tests every quarter to validate which channels actually drive new revenue vs steal credit.
Build a unit economics dashboard separating CAC, LTV, contribution margin, and payback by channel and cohort.
Establish a contribution margin floor for each channel — pause spend when margin drops below threshold for 14 days.