How much drywall should I remove around a moldy area?
The industry standards, the ANSI/IICRC S520 Standard of Care for professional mold remediation, generally stipulates removal of 24" around the visibly moldy area. We would also generally remove any other wet drywall. If you see visible mold on the room facing side of the drywall, the likelihood of the problem being worse inside the walls is high.