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How to calculate cost per acquisition

2026-05-20 11:26 · Paid Marketing

Learn the CPA formula, see a simple example, and understand how cost per acquisition fits into paid campaign reporting.

Cost per acquisition, usually shortened to CPA, measures how much ad spend is needed for one target action. That action can be a lead, signup, purchase, install, trial start, booking, or any conversion that matters to the campaign.

The CPA formula is:

CPA = ad spend / acquisitions

For example, if a campaign spends $3,000 and produces 150 leads, the CPA is $20.00. If an ecommerce ad set spends $1,200 and produces 40 purchases, the CPA is $30.00 per purchase.

The key is to define the acquisition clearly before calculating. Do not mix leads, purchases, and signups in the same CPA calculation unless you intentionally treat them as the same conversion type.

CPA helps marketers compare campaigns that have different traffic volume or click costs. A campaign with a higher CPC can still have a better CPA if the traffic converts well. A campaign with cheap clicks can still have a weak CPA if few visitors take action.

Use the CPA Calculator at /tools/cpa-calculator for quick checks. Then compare the result with CPC, conversion rate, CAC, ROAS, and ROI to understand whether the campaign is worth scaling.