Cost per acquisition (CPA)
Average ad spend for one named result, such as a purchase, signup, or lead. The result must be specified or the number means little.
See it
What it is
CPA is ad spend divided by the number of attributed acquisitions. Spend $1,000 and record 20 purchases, and purchase CPA is $50. The acquisition must be named because platforms also use CPA for leads, app installs, trials, or any other configured conversion. Google Ads turns the number into a control with its Target CPA bidding option, which tells the auction what one conversion is worth to you.
Use it to compare campaigns that pursue the same result and to ask whether paid acquisition can fit inside the value of that result. It is narrower than customer acquisition cost: CPA usually measures media spend against attributed conversions, while CAC can include salaries, tools, and sales costs across all new customers.
Gotcha: two CPA numbers are incomparable when the conversion event or attribution window differs. A cheap lead is not a cheap customer, and a platform-reported purchase is not automatically an incremental sale. Write the event, spend scope, attribution source, and date window next to the number.
Ask AI for it
Build a CPA calculator from Google Ads API fields `metrics.cost_micros` and `metrics.conversions`. Convert micros to the account currency, then compute spend divided by conversions for each campaign and conversion action. Show spend, conversions, CPA, date range, attribution source, and the exact acquisition event beside every row. Return `null` and display 'No conversions' when the denominator is zero; never divide by zero or replace it with 0 dollars. Add a separate blended row only when all included campaigns use the same event and window, and keep CPA distinct from fully loaded CAC.