CPA calculator
CPA is spend divided by conversions. A 1,000 budget producing 100 conversions is a CPA of 10. It works when CPA sits below the gross profit a conversion generates, not below some published benchmark.
How to calculate CPA
CPA is a product of two things — cost per click and conversion rate, and knowing which is responsible changes what you do. A CPA of 40 from a 2 CPC at 5% conversion is an entirely different problem from a 40 CPA from a 0.40 CPC at 1%. The first is an auction and bidding problem; the second is a landing page and offer problem. Reporting CPA without its two components is the most common way a marketing report manages to be accurate and useless at the same time.
Questions
Cost per acquisition: the ad spend required to produce one conversion.
CPA usually counts media spend against a specific conversion. CAC counts all sales and marketing cost against new customers won.
Up to the gross profit a conversion generates, or up to lifetime value if the customer is likely to return.
Split it into CPC and conversion rate. Whichever is out of line against your own history is the one to work on.
It should not. Mixing paid spend with organic conversions flatters the number and hides what more budget would actually cost.