Cobra Effect · People and organisations
Span of control
Why a manager can only really lead a handful of people.
7 cards, read aloud in 2:33, with a test and sources.
A manager with 4 direct reports gets promoted. Now she has 19.
Same person. Same hours. Same skill. Within a month the good ones have stopped hearing from her and the struggling ones go unnoticed. Nothing broke. The number did.
How many people can one person actually manage?
Lyndall Urwick asked it plainly in the Harvard Business Review in 1956. His answer was five, or at the most six, when their work interlocks. He offered it as a rule of thumb, and it has been argued over ever since.
The reason is not the people. It is the pairs between them.
In 1933 Vytautas Graicunas counted the relationships a manager has to hold in mind. Not one per person. Every pair, and every group. At five reports that comes to about 100 relationships. At six, over 200. Add one person and the job jumps.
So the right number is not a number. It depends.
If everyone does the same well understood job, one supervisor can carry 20 or more. If the work is new, tangled and changing, six is generous. Distance, experience and how much coordinating the work needs all move the line.
Too wide, and the manager becomes a bottleneck with a diary.
Decisions queue. Feedback stops. The quiet performer is invisible and the loudest problem takes the whole week. People start deciding without her, which is sometimes the best thing that could happen.
Too narrow is its own disease.
Give a manager 2 people and she will manage them very closely indeed. Narrow spans build tall organisations, and every layer adds a delay and a chance to misunderstand. A message that crosses 8 levels arrives as a different message.
The question to ask before you hand someone another report.
How much coordinating does this work need, and how much of it is already understood? Count the pairs, not the people. And if a manager says she is fine, ask her team when they last had her attention.
Sources
- Span of control, Wikipedia. The history from Sir Ian Hamilton and Graicunas through to Urwick, the factors that widen or narrow it, and why modern firms run wider spans than the old rules allowed.
- The Elements of Administration, Lyndall Urwick, 1943. Urwick setting out his principles of organisation, span of control among them. Dated in tone, and still the clearest statement of where the number came from.
- High Output Management, Andrew Grove, 1983. A working manager on how much of a manager’s output comes from a small number of people, and how many hours a week that actually costs in practice.
Nearby ideas
- Dunbar’s number. Why groups stop working the old way once they pass about 150.
- Brooks’s law. Adding people to a late project makes it later.
- The Ringelmann effect. The bigger the group, the less effort each person puts in.
- Broken windows theory. Visible neglect invites more of it, though the crime claims are contested.
- Parkinson’s law. Work expands to fill the time you give it.
- The Peter principle. Why people get promoted until they reach a job they cannot do.
- Conway’s law. Systems end up shaped like the teams that build them.
- The Hawthorne effect. Being watched changes what people do, and muddies what you measure.