CPA: definition, calculation and optimisation of cost per acquisition
Updated on February 22, 2026
Quick definition
CPA (Cost Per Acquisition) is the cost per acquisition that measures the average amount spent on marketing to obtain a specific conversion: a purchase, a sign-up, or a qualified lead. CPA is a fundamental KPI for evaluating the profitability of an ad campaign or acquisition channel.
How it works
Formula
CPA = Total marketing spend / Number of conversions obtained
Example: €2,000 spent on Google Ads for 40 sales = CPA of €50
CPA can be calculated at different levels: per campaign, per channel (SEA, social ads, email), or globally across all marketing spend. It is crucial to clearly define what counts as an acquisition: a purchase, a qualified lead, a paid sign-up? This definition entirely determines the relevance of the calculated CPA.
In programmatic advertising (Google Ads, Meta), there is a bidding strategy called Target CPA where the algorithm automatically optimizes bids to hit a predefined cost per acquisition.
To maximize the usefulness of CPA, systematically compare it to the average customer value (CLTV or AOV): a CPA of €80 is acceptable if the margin per sale is €200, but destructive if it is €60.
Why it matters
CPA is the central indicator of a digital acquisition strategy's profitability. Without an accurate CPA, it is impossible to objectively compare the profitability of different channels (SEA vs. social ads vs. SEO) and decide where to concentrate budget.
By setting a target CPA based on your margins, a marketing team can automatically exclude unprofitable campaigns and reallocate budget to the most efficient sources. CPA translates marketing performance into cost terms directly comparable to traditional sales costs.
How to improve or use it
- 1Improve the conversion rate of your landing pages to obtain more conversions on the same ad budget.
- 2Refine your targeting to reach more qualified audiences and reduce wasted spend.
- 3Use retargeting to recapture visitors who did not convert on first contact — their CPA is generally far lower than cold-acquisition CPA.
- 4Optimize ad quality to improve Quality Score (Google Ads) and reduce CPC.
- 5Test different channels and correctly attribute conversions to identify the most profitable sources.
With Sublim
By connecting Sublim to your conversion data, you can calculate your real CPA per traffic source, including organic channels often ignored by ad tools. Sublim's GDPR compliance ensures conversions are correctly attributed even for users without cookies — preventing you from underestimating your campaigns' profitability.
Frequently asked questions
What is the difference between CPA and CPL?
CPA (cost per acquisition) measures the cost of obtaining a final conversion (purchase, paid sign-up), while CPL (cost per lead) measures the cost of obtaining a qualified sales contact, such as a completed form or a demo request. CPL is a form of CPA applied specifically to lead generation.
How do I set a target CPA?
The target CPA is calculated by subtracting your desired margin from the average revenue generated by a conversion. For example, if your average order value is €150 and you target a 40% margin, the revenue available for acquisition is €90. Your target CPA must therefore not exceed €90 to remain profitable. Refine this calculation by including LTV if you have a recurring revenue model.
Can CPA be used to measure non-commercial conversions?
Yes, CPA applies to any action defined as a goal: whitepaper download, webinar registration, app install. In these cases, it is sometimes called cost per action. The key is to value the target conversion in order to assess whether the resulting CPA is acceptable relative to the value generated.
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