What is cost per acquisition (CPA)?
CPA (cost per acquisition) is how much you pay, on average, for each conversion your ads generate. Ad platforms like Google and Meta report CPA (or "cost per result") for whatever action you optimized for — a purchase, signup, or lead.
CPA = Ad spend ÷ Acquisitions (conversions)
Spend $3,000, get 120 conversions → CPA = $3,000 ÷ 120 = $25. Each conversion cost you $25 in media spend.
How to calculate CPA (step by step)
- Get your ad spend — total spend on the campaign or channel in the date range.
- Get your conversion count — match the same date range and attribution window as the platform.
- Divide spend by conversions — that's your CPA.
Be consistent with attribution. If your ad platform counts view-through conversions and you only count click-through, your numbers will differ. Use the same window for both.
Worked example: ecommerce purchase CPA
A DTC brand running Facebook ads for online orders:
| Metric | Value |
|---|---|
| Monthly ad spend (Facebook) | $7,500 |
| Purchases attributed (7-day click) | 250 |
| CPA | $30.00 |
| Average order value (AOV) | $75 |
| Gross margin | 50% |
| Gross profit per order | $37.50 |
| Net per order (before overhead) | $7.50 |
At $30 CPA and $37.50 gross profit per order, each acquired customer generates $7.50 to cover overhead and profit. If the brand could improve conversion rate from 2% to 2.5%, the same $7,500 spend would drive ~312 purchases — dropping CPA to ~$24 and raising net per order to $13.50. That's why CRO and CPA are always worked together.
Worked example: B2B lead-gen CPA
A SaaS company running LinkedIn ads for demo requests:
| Metric | Value |
|---|---|
| Monthly ad spend (LinkedIn) | $12,000 |
| Demo requests (leads) | 80 |
| CPA (demo request) | $150.00 |
| Demo-to-close rate | 20% |
| Implied customer CPA | $750 |
| Customer LTV (gross profit) | $3,600 |
| LTV:CAC (media-only) | 4.8:1 |
A $150 cost per demo request looks expensive in isolation, but it converts into a healthy 4.8:1 LTV:CAC after factoring in close rate. In B2B, always read CPA against the full funnel — a high lead CPA can still be a great business if close rate and deal size are strong.
CPA vs. CPL vs. CAC
These terms overlap but mean different things depending on context:
- CPA (this calculator) — cost per ad-reported conversion. The conversion type depends on your campaign goal.
- CPL — cost per lead specifically (form fill, demo request).
- CAC — cost per paying customer, usually with fully-loaded sales & marketing cost.
If your ad optimizes for purchases, CPA ≈ CAC (media only). If it optimizes for leads, CPA ≈ CPL. Always match the acquisition count to what the platform actually counted.
How to use CPA
Compare CPA to the value of each acquisition. For ecommerce, if CPA is $25 and AOV is $80 at 50% margin, you keep $15 gross profit per order before overhead — likely profitable. For lead gen, compare CPA to expected customer value × close rate.
How to lower CPA
- Improve CTR with better creative and targeting.
- Improve conversion rate on landing pages — same clicks, more conversions.
- Pause high-CPA placements and audiences — shift budget to what's working.
- Raise offer value with upsells and bundles so each conversion is worth more.
- Test different campaign objectives — the platform optimizes toward what you tell it to.
CPA optimization is usually the highest-leverage marketing work because it compounds: lower CPA + higher conversion value = dramatically better unit economics.