Cost per acquisition or CPA is the total amount invested into promoting a website to get one sale. To calculate CPA in a Google Ads campaign, we must divide the total cost of the campaign (both the investment and the management fees) by the total number of conversions. In case of recurring purchases (on average, a customer makes more than one purchase in a specified period), CPA is lower than the customer acquisition cost or CAC, as it would be equal to this customer’s acquisition cost divided by the average transactions made by each customer.