For most online businesses, the principle behind a cost-per-acquisition model is fairly straightforward. To find the total costs of customer activity in a period, divide the costs of visits in that period by total sales.
For example, if you're looking at the cost per acquisition of your PPC activity, take the total amount of your PPC ad spend and divide by the number of sales and you get cost per acquisition.
This is all very easy to understand, but problems arise when you start to add some complexity. And as more retailers adopt an omnichannel commerce model, the level of complexity in both the customer journey, and how merchants undertake attribution modeling, increases considerably.
Learn more here.