Cost per acquisition
CPA / cost per action / cost per conversion / cost / conv.
Cost per acquisition is what you paid for each counted conversion, spend divided by conversions. Google expands the abbreviation as cost per action, not acquisition. It inherits whatever your conversion column counts, so two businesses can report the same figure and mean entirely different things.
The arithmetic is the easy part. Google defines average CPA as the average amount you have been charged for a conversion from your ad, calculated by dividing the total cost of conversions by the total number of conversions. Its own example is two conversions, one costing 2 dollars and one costing 4, giving an average CPA of 3. Microsoft writes the same thing as a formula, spend divided by conversions, and shows it as cost per conversion.
Start with the abbreviation, because it is not what most people think. Google's page is titled Average CPA and expands it as cost per action. Not acquisition. That is not pedantry: an action is whatever you told the platform to count, and an acquisition sounds like a customer. The looser word is the accurate one.
Which leads to the thing that actually matters. This number has no meaning on its own, because the denominator is a choice. If your conversion column counts phone calls, form fills and newsletter signups together, your cost per acquisition is an average across three very different events. Change what counts and the figure moves without anything changing in the business.
One more caution worth stating plainly, because you will not find it said elsewhere. There is no independent standard for this metric. No standards body, regulator or professional institute defines cost per acquisition. Every definition available comes from a company selling advertising. That does not make the platforms wrong, but it does mean there is nothing above them to appeal to when two numbers disagree.
In practice
Two contractors both report a 60 dollar cost per acquisition. The first counts only booked jobs. The second counts every form submission, including the ones that never answer the phone afterwards. The first number describes the cost of work won. The second describes the cost of an email address. Identical figures, and one business is roughly ten times healthier than the other.
Not the same as
- Cost per click
- You pay for clicks whether or not anything follows. This counts only the ones that produced a recorded action.
- What a customer costs you
- That requires knowing how many recorded actions become paying work, which no ad platform can see.
Why it matters to you
This is the figure most often quoted to prove advertising is working, and it is the easiest to improve without improving anything. Adding a lighter conversion action lowers it immediately. Before comparing it to a benchmark, a previous month, or another supplier's number, the only question worth asking is what is being counted underneath it.
What is typical
There is no benchmark worth quoting, and no independent body defines this metric. Two businesses with identical figures can be counting entirely different events, so an industry average for it carries almost no information.
What to ask or check
- 01Exactly which actions are inside the conversion count this figure divides by?
- 02Has that list changed during the period being compared?
- 03What share of those counted actions turned into paid work?
What people get wrong
That CPA stands for cost per acquisition and describes the cost of winning a customer. Google expands it as cost per action, and an action is whatever was configured to count, which is usually an inquiry rather than a sale.
Red flags
- A cost per acquisition compared across months without confirming the conversion list was unchanged.
- A falling figure presented as improvement, when a lighter conversion action was added.
- An industry benchmark quoted for it, given no standard body defines the metric.
Where you will see it
As Cost / conv. in Google Ads, and as cost per conversion in Microsoft Advertising reports.