CPA

Cost per Acquisition

Quick definition

Cost per acquisition (CPA) is the average cost of each conversion you have defined, calculated as advertising cost divided by the number of conversions.

Formula

CPA = Advertising Cost ÷ Conversions

Formula variables

Advertising Cost
The spend on the ads, campaign or channel being measured.
Conversions
The number of times the chosen action (a purchase, signup or other goal) was completed in the same period.

Worked example

Advertising cost
$3,000
Conversions
120

3,000 ÷ 120

Result: $25

Each conversion cost $25 on average. The figures are illustrative.

How definitions differ

What counts as an acquisition
CPA = Advertising Cost ÷ Conversions
CPA is the cost of whatever action you define as a conversion. It can be a purchase, a signup, an app install or a lead. The abbreviation is also read as cost per action. State the action you counted.
Platform conversion settings
Ad platforms report their own cost-per-conversion figures. These depend on which conversions are counted, how they are attributed and how long after a click they are credited, so they may not match your analytics.

How to interpret it

CPA shows how efficiently spend produces the action you chose. It is only as meaningful as that action: a cost per signup says nothing about whether signups become paying customers.

When the conversion is a new paying customer, CPA is close to customer acquisition cost, but CAC normally includes more costs than ad spend.

When it is useful

  • Comparing campaigns, audiences or creatives on the cost of reaching a goal.
  • Setting a target cost for automated bidding, where the platform supports it.
  • Checking whether rising costs come from the price of clicks or from falling conversion.

Limitations

  • The result depends on the conversion definition and the attribution method.
  • Different conversion actions have different value, so CPA across them is not comparable.
  • Ad-platform and analytics figures often differ.

Common mistakes

  • Treating CPA and CAC as the same thing.
  • Mixing different conversion types into one CPA.
  • Comparing platform-reported CPA with analytics-reported CPA without noting the attribution difference.

Related KPIs

Related marketing terms

Related tools

Campaign URL Builder

Marketing

Conversions can only be credited to a campaign if visits are tagged. The builder adds consistent campaign parameters to your links so analytics can group conversions by campaign; it does not calculate CPA.