Advertising & ROAS
What Is Cost Per Acquisition (CPA)?
A clear guide to CPA for marketers: formula, CPA vs CAC, how to set targets, and when campaign-level cost per acquisition is the right metric.
Cost Per Acquisition (CPA) is the average amount you spend in advertising to generate one conversion. That conversion might be a purchase, lead, free trial, or another defined action—scoped to a campaign, ad set, or channel. CPA is the day-to-day metric media buyers use to optimize spend.
How to use the CPA Calculator
- Open the CPA Calculator.
- Enter total ad spend for the campaign or channel.
- Enter the number of conversions in the same period.
- Compare CPA to conversion value, AOV, or LTV to judge profitability.
The CPA formula
CPA = Total Ad Spend ÷ Conversions
Example
| Input | Value |
|---|---|
| Campaign ad spend | $12,000 |
| Conversions (trial starts) | 240 |
| CPA | $50 |
CPA vs CAC
| Dimension | CPA | CAC |
|---|---|---|
| Scope | Campaign / channel | Business-wide |
| Costs | Usually ad spend | Fully loaded acquisition |
| Cadence | Daily / weekly | Monthly / quarterly |
| Audience | Media buyers | Founders, finance, investors |
If only 20% of those trials become paying customers, the paid-channel contribution toward CAC is roughly $50 ÷ 0.20 = $250 before overhead. See CAC vs CPA for the full distinction.
What is a good CPA?
There is no universal target. A “good” CPA is below the economic value of the conversion after margin and downstream conversion rates. Ecommerce teams often compare CPA to contribution margin per order; SaaS teams compare against LTV and trial-to-paid rates.
Common CPA mistakes
| Mistake | Why it hurts |
|---|---|
| Comparing CPA across different conversion events | Leads ≠ purchases |
| Ignoring lead-to-customer rates | Low CPA can hide expensive CAC |
| Reporting CPA as CAC | Overstates unit economics |
| Mixing attribution windows | Inflates or deflates results |
Related reading
- CAC vs CPA comparison
- What is CAC
- CPC, CPM & CTR guide
- What is ROAS
- CPA Calculator · CAC Calculator · ROAS Calculator
Sources
Directional CPA and CAC guidance here follows common paid-media and SaaS practice. For industry research context, see public materials from OpenView and platform help docs (Google Ads, Meta). Always validate against your own conversion economics.
Frequently Asked Questions
What is CPA?
CPA (Cost Per Acquisition or Cost Per Action) is the average ad spend required to generate one conversion—such as a lead, signup, trial, or purchase—within a campaign or channel.
How do you calculate CPA?
CPA = Total Ad Spend ÷ Number of Conversions for the same campaign and time window. Example: $10,000 spend and 200 conversions = $50 CPA.
What is the difference between CPA and CAC?
CPA is usually campaign-level and media-only. CAC is business-level and fully loaded (ads plus sales, tools, and overhead). Mixing them up overstates efficiency.