I’ve never been able to find any detailed information about the expected size of the SCCM database. I decided to keep track of this during a recent deployment.
As a general rule, I had usually allowed 500MB for SCCM system database and about 2-5MB for each client that is deployed. Since there are no definative guidelines in the SCCM capacity planning documentation, I decided to closely track the database size on this SCCM deployment.
In summary I found that you should allow 500MB for system databases, then allow 5MB for each client you are going to deploy. This number allows space for SQL data and log files. My deployment included almost all features of SCCM including OSD (many driver packages), Software Updates, approx 200 software packages and around 15 secondary sites.