Google CPA: Average Cost to Acquire a Purchase

Google CPA measures how much you spend on average to drive each purchase through Google Ads—lower is better.

Formula

Google CPA = Google Spend ÷ Google Purchases

Formula Components

Metric	Definition
Google Spend	Total amount spent on Google advertising
Google Purchases	Number of purchases attributed to Google Ads

Metadata
Type	Currency
Data Source	Google Ads
Aggregation	Ratio

Example

A home goods store spent $4,200 on Google Ads in March and drove 84 purchases:

Metric	Value	Calculation
Google Spend	$4,200	—
Google Purchases	84	—
Google CPA	$50.00	$4,200 ÷ 84

How It Works

Google CPA divides your total Google ad spend by the number of purchases attributed to those ads. This gives you the average cost to acquire each conversion, helping you understand campaign efficiency at a glance.

When to Use

Scenario	Action
Comparing campaign efficiency	Lower CPA campaigns deliver purchases more cheaply
Setting bidding targets	Use historical CPA to inform target CPA bidding
Budget allocation	Shift spend toward campaigns with better CPA
Evaluating profitability	Compare CPA against average order margin

Metric	Relationship
Google Cost per Purchase	Same calculation—CPA is a common abbreviation
Google ROAS	Efficiency from the revenue perspective
Google Spend	Numerator in the CPA formula
Google Purchases	Denominator in the CPA formula

See all Google Efficiency metrics →

Google ROAS Google Cost/Purchase

⌘I

​Formula

​Formula Components

​Example

​How It Works

​When to Use

​Related Metrics

Formula

Formula Components

Example

How It Works

When to Use

Related Metrics