What is CPA? Cost per acquisition explained
CPA, or cost per acquisition, is the average ad spend it takes to win one conversion, whether that is a purchase, lead or sign-up. Here is what CPA means, how to calculate it, a worked example and how to tell whether yours is good.
CPA, or cost per acquisition, is the average ad spend it takes to win one conversion: a purchase, lead, sign-up or install, depending on what you track. Divide spend by conversions. It is the core efficiency metric for campaigns where every conversion has a similar value, and the basis of target CPA bidding in ad platforms.
How do you calculate CPA?
| Metric | Formula |
|---|---|
| CPA | Ad spend ÷ conversions |
| CPA from the funnel | Cost per click ÷ conversion rate |
| Break-even CPA | Contribution per conversion |
The second line shows why CPA moves: if clicks cost more or fewer clicks convert, CPA rises. In Google Ads, the target CPA bid strategy sets bids around a target, which Google describes as "the average amount you'd like to pay for a conversion".
CPA example
Illustrative figures for a UK online course provider:
- Ad spend: £8,000. Clicks: 4,000, so cost per click is £2.00.
- Conversion rate: 4%, so 160 enrolments.
- CPA: £8,000 ÷ 160 = £50, the same as £2.00 ÷ 0.04.
Each enrolment sells for £180 net of VAT with £30 of variable costs, so break-even CPA is £150 and the campaign keeps £100 per sale after ads.
What is a good CPA?
Any CPA below your break-even CPA, the contribution one conversion brings in. For lead generation there are published reference points: WordStream's 2026 Google Ads benchmarks, based on 13,474 US search campaigns from April 2025 to March 2026, put the median cost per lead at $66.69. Costs vary widely by industry and country, so start from your own margin.
CPA vs CAC and ROAS
- CAC counts only new customers and often includes salaries and tools, while CPA counts any tracked conversion from ad spend.
- ROAS is the better measure when conversion values vary, as with ecommerce baskets of different sizes.
- Your attribution model decides which conversions each channel gets, so CPA by channel changes with it.
How Grower helps
Grower's channels leaderboard ranks connected channels by ROAS, conversions, cost, CPA, impressions and CTR, and the performance spotlight highlights your best CPA. Conversion and budget analyses on any campaign come with suggested actions you approve, dismiss or turn into a task.
Frequently asked questions
Is CPA the same as cost per lead?
Cost per lead is a type of CPA where the conversion is a lead, such as a form fill or call. CPA is the general term and covers any action you choose to track: purchases, sign-ups, app installs or demo bookings. When you report CPA, name the conversion, because a £20 CPA for leads and a £20 CPA for sales mean very different things.
How do you lower CPA?
Work on its two drivers: cost per click and conversion rate. Tighten targeting and add negative keywords to cut wasted clicks, refresh tired creative to lift click-through rate, and improve landing page speed, offer and form length to convert more visitors. Check that conversion tracking is complete too, since missing conversions inflate CPA.
Should I use target CPA or target ROAS bidding?
Use target CPA when conversions are worth about the same, such as leads or sign-ups. Use target ROAS when values vary, as with ecommerce orders, because it can pay more for bigger baskets. Both need reliable conversion tracking, and target ROAS also needs accurate conversion values. Set either target from your margin, not from a benchmark.
Find your profit line with the free break-even ROAS calculator, then book a demo to see CPA for every connected channel in one leaderboard.