As I could not find that number on the net, I started to count them.
Just so we don't forget, the total number of rules is 351 rules. See details below.
A) For FxCop, as per today
The number of rules is given at the end of the line, and totals to
Correct library design as specified
by the .NET Framework Design Guidelines.
2 Globalization Rules (07)
World-ready libraries and applications.
3 Interoperability Rules (16)
Interacting with COM clients.
4 Maintainability Rules (03)
Library and application maintenance.
5 Mobility Rules (02)
Mobility warnings support
efficient power usage.
6 Naming Rules (20)
Adherence to the naming conventions
of the .NET Framework Design Guidelines.
7 Performance Rules (18)
High performance libraries
8 Portability Rules (02)
Portability warnings support
portability across different platforms.
9 Reliability Rules (05)
Library and application reliability,
such as correct memory and thread usage.
10 Security Rules (28)
Safer libraries and applications.
11 Usage Rules (37)
Appropriate usage of the .NET Framework.
B) For StyleCop 4.3 we have 7 Categories.
The number of rules is given at the end of the line, and totals to 154 rules.
1 Documentation Rules (48)
2 Layout Rules (17)
3 Maintenability Rules (11)
4 Naming Rules (11)
5 Ordering Rules (14)
6 Readability Rules (25)
7 Spacing Rules (28)
Calculation of the Maintainability Index :
Maintainability Index = 171 - 5.2 * ln(Halstead Volume) - 0.23 * (Cyclomatic Complexity) - 16.2 * ln(Lines of Code)