CPA (cost per acquisition) is what you pay in advertising for one conversion. You calculate it as ad spend divided by the number of conversions in the same period. For an online store that is the cost per order, for a service business the cost per lead. A CPA of €10 means each order cost €10 in ads.
CPA (cost per acquisition) is what you pay in advertising for one conversion. You calculate it as ad spend divided by the number of conversions in the same period. For an online store that is the cost per order, for a service business the cost per lead. A CPA of €10 means each order cost €10 in ads.
You will also see it spelled out as cost per action; the meaning is the same. In Google Ads it is the “Cost / conv.” column, in Meta Ads it shows up as cost per result. The number is only as good as what the ad platform counts as a conversion. Once add-to-carts or contact clicks get mixed in, CPA looks cheap and tells you nothing.
Divide spend for a period by conversions for the same period and the same campaigns. You can get the same number from the other side: CPA equals cost per click divided by conversion rate. That is why there are only two ways to lower it, a cheaper click (CPC) or a higher conversion rate.
| CPA | spend ÷ conversions | Example: €2,000 spend ÷ 200 orders = €10 |
| CPA from CPC | CPC ÷ conversion rate | Example: €0.25 ÷ 2% = €12.50 |
| Maximum CPA | average order value × margin | Example: €50 × 30% = €15 |
The third row is the line above which an order from ads loses money, often called break-even CPA. It is the same idea as break-even ROAS, expressed in money per order instead of a percentage.
Move the sliders to match your account. You will see your CPA, the ceiling your gross margin allows, and what each order leaves you after the ads are paid.
An industry average won’t answer this. A good CPA is one that sits below your own ceiling: average order value excluding VAT times gross margin. A store with a €50 average order and a 30% margin can afford at most €15 per order. At a €10 CPA it keeps €5 from each order; at €18 it loses money on every one.
Set your target CPA below that ceiling by the profit you want to keep. For lead generation, start from the value of a lead: average deal × margin × the share of leads that become customers. And if customers come back, you can pay more for the first order than it earns. How much more is what CLV tells you.
In the accounts we manage, we lower CPA through campaign structure and clean measurement, not by cutting budgets. At Vše pro pejska the cost per order from ads fell 25% year over year while spend was down 1% (Google Ads, 9 Oct 2025–19 Sep 2026, case study). At Letsport the cost per purchase fell 40% between the 30 days before we took over and 30 days in September (Google Ads, 29 Mar–27 Apr vs 27 Aug–25 Sep 2026, case study).
CPA tells you what one order costs. It doesn’t tell you what the order earned. In a store where baskets differ by tens of euros, pair CPA with ACoS or ROAS, which take order value into account. Customer acquisition cost (CAC) is a broader idea: it counts every acquisition cost, not just ads, and divides only by new customers.
| Metric | Formula | What it answers | When to use it |
|---|---|---|---|
| CPA | spend ÷ conversions | What one order or lead costs | Lead gen, stores with similar order values |
| CPC | spend ÷ clicks | What one visit from ads costs | Checking the auction and competition |
| ACoS | spend ÷ revenue × 100 | What share of revenue goes to ads | Stores, talking to finance |
| ROAS | revenue ÷ spend × 100 | Revenue per unit of ad spend | Target for automated bidding in ecommerce |
| CAC | acquisition costs ÷ new customers | What a new customer costs in total | Growth planning alongside CLV |
Metrics that show up in the same sentence as CPA.
CPA is a ratio, and the denominator decides everything. When campaigns count add-to-cart as a purchase, CPA drops to a fraction and looks great. At Papírnictví VojTech only 8% of reported conversions in March 2026 were real purchases; the rest were carts and a duplicate tag (case study). Our rule: the primary conversion is a purchase only, or a submitted lead or call for services.
A €12 order and a €200 order carry the same weight in CPA. A target CPA then pushes the system toward cheap baskets. In a store with a mixed range, bid to a return target and keep CPA as a control number.
Google Ads, Meta and GA4 each credit conversions by their own rules, so one purchase can be claimed by several systems at once. Attribution explains the gaps. The order count in your store’s back office is what decides, not the sum of what the platforms claim.
Each conversion, usually an order or a lead, cost €10 in ads on average. Whether that is a lot depends on order value and margin. With a €50 average order and a 30% margin the ceiling is €15, so €10 is fine.
Multiply average order value excluding VAT by gross margin. The result is what an order can carry in ad cost without a loss. Your target CPA should sit below it by the profit you want to keep.
CPC is the price of one click, CPA the price of one conversion. Conversion rate links them: CPA = CPC ÷ conversion rate. A cheap click with a low conversion rate can end up as a more expensive order than a pricey click that sells.
No. CPA divides ad spend by all conversions, including repeat orders from existing customers. CAC takes every cost of winning a customer and divides it by new customers only, so it is usually higher.
An automated bidding strategy that aims for the average cost per conversion you set. It works only as well as your measurement: if add-to-carts sit among primary conversions, the system learns to find people who add to cart, not people who buy.
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