Quick answer
Cost per acquisition (CPA) is the average marketing cost of one conversion, calculated as the spend on a campaign or channel divided by the number of conversions it produced, where the conversion is a defined action such as a purchase, sign-up or lead.
Formula: CPA = marketing spend / number of conversions
What is cost per acquisition?
Cost per acquisition (CPA) is the average amount you spend in marketing to get one conversion:
CPA = marketing spend / conversions
"Acquisition" is whatever action you define as the goal: a purchase, a trial start, a sign-up or a qualified lead. Always say which one, because a $5 CPA for newsletter sign-ups and a $50 CPA for purchases are not comparable.
CPA vs CAC vs CPL vs CPC
| Metric | Formula | Scope |
|---|---|---|
| CPC | Spend / clicks | One ad click |
| CPL | Spend / leads | One lead |
| CPA | Spend / conversions | One conversion of a chosen type, usually media spend only |
| CAC | All acquisition costs / new paying customers | Fully loaded: media, salaries, tools, all channels |
A sample channel comparison
One month of paid channels, conversion = purchase (sample numbers):
| Channel | Spend | Purchases | CPA | Revenue | ROAS |
|---|---|---|---|---|---|
| Search ads | $6,000 | 150 | $40 | $18,000 | 3.0 |
| Social ads | $4,000 | 200 | $20 | $6,000 | 1.5 |
| Affiliates | $2,000 | 40 | $50 | $9,600 | 4.8 |
Social has the lowest CPA, but each purchase is worth only $30 on average, against $120 for search and $240 for affiliates. Judged by ROAS, affiliates return the most per dollar despite the highest CPA. CPA alone would have pointed budget the wrong way.
What is a good CPA?
A good CPA is one that leaves profit after the conversion's value:
- For e-commerce, compare with average order value × margin, plus repeat purchases if you can count on them.
- For subscriptions, compare with customer lifetime value; a common rule of thumb is LTV at least three times the acquisition cost.
- Industry benchmarks vary widely by country, product price and conversion definition, so your own trend matters more.
Five ways to lower CPA
- Raise landing-page conversion. Doubling the conversion rate halves CPA at the same spend.
- Cut wasted spend. Exclude irrelevant search terms, placements and audiences.
- Match message to intent. Send each ad to a page that answers exactly what it promised.
- Shift budget to efficient campaigns, judged on value as well as cost.
- Measure conversions completely. Missing conversions (blocked scripts, cross-device) inflate CPA on paper; server-side purchase events help.
CPA in TapCub
TapCub's Channel ROI page (All-platform analytics › Business › Channel ROI) computes cost per acquisition as spend divided by conversions, where conversions are purchases on the order ledger, alongside cost per click (spend ÷ sessions) and return on ad spend. Spend is entered on the Costs tab, one row at a time or by CSV with the columns day, channel, source, campaign, cost, currency, clicks and impressions; you can group by channel, source or campaign. Without imported spend, the cost metrics stay empty. To see which touches led to those purchases, use attribution.
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