The total amount that a single customer can spend in a given period of time for a category of services (i.e. their budget). This metric is important because it gives a sense of the financial capabilities of your customers, and it allows an observer to judge how expensive your product is relative to a customer’s appetite. Startups that charge a small amount compared to the average wallet size are just as risky as those that charge a very high proportion of the wallet size as their product’s price. You don’t generally want to be insignificant, nor do you want to be so large that you knock out an entire budget.