What is Cost Per Acquisition (CPA)?
CPA is the total amount spent on advertising divided by the number of people who click the ad AND then make a conversion on your website.
Why is it helpful to measure CPA?
Cost Per Acquisition lets you know exactly how much it costs to gain one new customer with your ad campaign. If your campaign goal is to drive conversions, understanding how much you will have to spend to get "x" number of conversions will be helpful.