How long can I stay with my visitor/tourist/business visa in Germany and the Schengen states?
The visa sticker itself stipulates how many days in the given period you can stay in Germany and the other Schengen States. The maximum, should your visa stipulate this, is 90 days in any 180 days period. The visa sticker also stipulates how many times you are allowed to enter the Schengen area (1, 2 or multiple entries).
You may find more information and a short-stay calculator on the webpage of the European Commission.