I have been running a survey on Linked In on the size of central KM teams vs the size of the organisation they serve, just as a way of benchmarking team size for some of our clients.
I had been expecting to find a linear relationship, based on experience to date, or possibly a linear relationship with a minimum and a maximum.
The results from 41 datapoints are shown below, followed by analysis.
A couple of disclaimers before I get into analysis. Firstly the names of the companies has to remain anonymous. Secondly there are some very small teams, such as the lone guy in the 100,000-strong organisation, who is just starting on the KM journey and is not yet up to strength. Therefore the graph does not consist only of mature, full-strength teams. Thirdly the definition of "Knowledge Management" varies considerably - from companies that focus on learning from experience and communities of practice, to companies for whom KM means content management and librarianship. Finally there is FAR MORE to success in KM than just the size (or even the make-up or the leadership) of the team.
My expectation of a linear relationship was not met. Instead you can make a case for two linear relationships.
There is certainly a set of data which form a linear trend (blue in the diagram) representing one KM team member for every 5000 staff. The companies that I know on this trend have KM teams that I would call Catalytic teams; focusing on change management, on introducing the elements of KM into the business, and on change management. All of these are western companies.
There is another set of data which form a far steeper and less defined trend (red in the diagram), representing one KM team member per 500 staff. I am less familiar with many of these companies, but from the replies I have received, these teams act as Support teams, in that the members provide KM support services to the business, rather than expecting the business to support itself. Often these services seem to revolve around content management. The KM teams play the Knowledge Manager role, rather than supporting the Knowledge Managers in the business, and in addition may contain web developers, eLearning specialists, and others who create, format or package content. When I was in BP Norway as Knowledge Managers, I played this role, spending one third of my time on it for 100 staff.
So my conclusion from this is that the ideal size of your KM team depends on the role it will play. If it is a change management team, expecting the business to "do" KM, then 1 team member per few thousand employees is a good ration. If the team will "do" KM services or content management services themselves, then the ratio needs to be greater by a factor of 10.
If anyone has more datapoints to add, please comment here, or email me, so I can continue to build the dataset.