CPO vs CPA

Cost per order is simply the average amount of money a company spends to get anyone to purchase, while cost per acquisition is the average amount of money a company spends to get someone new to purchase.

Here's Sean on when to use each metric and a few things to be aware of when you're using CPO and CPA:

CPO Formula

CPA Formula

More on CPO and CPA

For an article on CPO, CPA, and ROAS (and to learn what a good CPO is) head over here.