It’s all over the board. The average for a typical application is probably between 100-1000 rules. I know of some customers working with tens of thousands of rules, which they manage by collecting them into different groups that apply to sub-cases. You can assign people to work on one or another area of rules. The biggest case I ever heard of was around 100,000 rules being managed by a national healthcare payment service that had special rules for many care providers. At the other end of the spectrum, some companies use rule software even when dealing with just a few rules. This would be the case when the rules are called upon by several applications, so separating them out and having them execute consistently and be managed in one spot is a benefit. Or when the rules change so frequently that it would be too hard to keep updating program code (even for relatively small changes).