Definition CPA is the core financial metric of ad efficiency. The conversion definition varies by campaign: form submit, purchase, subscription, or call. Target CPA (tCPA) serves directly as a bidding strategy.
How it works The system aggregates total ad spend within a date range. Conversion count is measured in the same window. Spend divides by conversions to produce average CPA. In the target CPA bidding strategy, Google Ads machine learning bids per auction toward the target. Actual CPA fluctuates around the target; sparse data causes long early volatility.
Where you see it in Scope Trends **Ad Command Center** > **CPA** shows CPA at campaign, ad group, and keyword level. The **Attribution Models** report compares CPA impact across models.
Frequently asked questions **When to adjust target CPA?** After the campaign collects 30+ conversions. Early changes reset the learning phase.
**Is CPA the same as CAC?** No. CPA is the cost per single conversion; CAC (Customer Acquisition Cost) divides all marketing and sales spend by new customer count.