Free tool
CPA Calculator
Work out what each customer costs you to acquire. Enter any two values in a section and the calculator fills in the third.
Total ad spend
Cost per acquisition
Is it profitable? (optional)
What is cost per acquisition?
Cost per acquisition (CPA) is the average amount you spend to win one customer, sale or lead. It tells you whether a campaign is buying results at a price the business can afford, not just whether it is generating clicks.
You can measure CPA across all marketing combined, or channel by channel (paid search, paid social, display) to see which one buys customers most cheaply.
How to calculate CPA
Start with total ad spend:
total ad spend = number of clicks × average CPC
Then divide it by the conversions that spend produced:
CPA = total ad spend ÷ total attributed conversions
Worked example
A campaign gets 8,000 clicks at an average CPC of £1.25, so total ad spend is 8,000 × £1.25 = £10,000. It drives 250 sales, so the CPA is £10,000 ÷ 250 = £40. If the average sale is worth £120, each acquisition leaves £80 and the campaign returns £3 for every £1 spent (a ROAS of 3.0×).
How to read your CPA
A CPA only means something against the value of what you acquired. If it sits above your average order value or lead value, the campaign loses money on every conversion. If it sits below, the gap is your margin.
CPA moves with two levers: what you pay per click, and how many clicks convert. A high CPA caused by a low conversion rate is usually a landing page or offer problem, not a bidding problem. Cutting CPC will not fix it.
Paid CPA also sets a useful benchmark for organic work. Customers won through SEO and AI search carry no per-click cost, so every conversion they deliver lowers the blended CPA across the business.
FAQs
What counts as an attributed conversion?
A conversion your analytics or ad platform credits to the campaign: a purchase, booking, enquiry or sign-up. Different attribution models (last click, data-driven) credit conversions differently, so the same spend can show different CPAs depending on the model.
What is the difference between CPA and CAC?
CPA usually covers media spend for a specific campaign or channel. Customer acquisition cost (CAC) is broader and includes salaries, tools and agency fees, so CAC is normally higher.
What is a good CPA?
There is no universal figure. A good CPA is one comfortably below the value of the customer it acquires. Compare it with your average order value, or with customer lifetime value if customers buy repeatedly.
Can CPA be used outside digital marketing?
Yes. Divide the cost of any campaign (print, events, direct mail) by the customers it brought in. The difficulty offline is attribution: proving which customers came from which activity.