Full Time Employees Per Number of Database Users? FTE/DB users? How Many Servers are too much to Handle?

After several days research, I have been trying to get a rough estimate on how many Full Time Employees are allocated per number of database users and/or servers.

Yes, I understand there are so many variables, considering that one database can be left alone for years perhaps thanks to proper maintenance built-in by the developers or the vendor, whereas another can require constant care -  but my question to the DBA Community out there, do you have any calculations used or hard-fast rules regarding the number of Database Users per DBA or Number of Servers per DBA to manage without high downtime risk?

Here are the answers and comments I received on the SQL Server Central version of this Blog

Posted by evangeld77 on 7 September 2011

Excellent question. I've been researching the same thing and here are my findings:
There are many white papers seeking to prove which database platform is less expensive to own. Regardless of their conclusion, they seem to use an estimate of 10 - 15 minutes per database, per day. That translates to around 32 databases for a full time DBA.
Rationalize that number with the ratios of production databases to test and development, etc.
I hope that helps. I'm open to other ideas.

Posted by dooncomputer on 5 October 2011

So far, I am able to find following breakdown:
• Average is 40 databases / DBA
• Lowest is 8 databases / DBA (Large Organization)
• Highest ratio is 275 databases / DBA
Anyone else has any comment/suggestion?

Posted by dooncomputer on 5 October 2011

Ooh, I must add we are not even close to high ratio..

Posted by Hugo Shebbeare on 19 October 2011

Thank you both very much for the input! Sorry I have not replied earlier, so much maintenance and Mirroring documentation documentation to do for research grants it has become overwhelming :S
Currently, I am responsible for about 350 user databases at around 5TB (when behaving and under control).
Thankfully there are three monitoring systems (SCOM, Spotlight, SQLResponse) to help out and a couple of other cross-trained Oracle/MySQL DBAs that can take the spill over, otherwise the scary FTE DBA/database ratio would be unmanageable.
I feel lucky considering that I had a friend who was put in front of 225 instances once, but he did not stay long in that organisation due to the stress of putting our fires constantly.

Posted by DBSlave on 28 November 2011

I think following is not the case we discussed here. You could "managed" 500+ SQL servers, leave them without real administrated, but just do your fire fighting on demand all day around... :)

Posted by Hugo Shebbeare on 11 December 2011

Exactly DBSlave, pro-active management cannot be done when you get over 200 instances - my friend who tried to 'survive' with a large firm that had been used as the outsourced DBA group ('group' being the real joke!) burnt out within a year of trying to put out fires all the time.