Definition
Customer acquisition is the work of turning people who don't know you into paying customers, through marketing, sales and the product itself. Its cost is measured as customer acquisition cost (CAC).
Formula
CAC = sales and marketing spend in a period ÷ new customers won in that period.
Judging channels
Compare channels on more than sign-ups: activation, retention and revenue of the customers each brings. A channel with fewer but longer-lasting customers is often worth more. See customer acquisition strategies.
Measuring it
Every new user needs a source, from UTM tags or the referrer, carried from their first visit to their sign-up. Then funnels and retention can be broken down by source.