You hear of project managers that manage multiple large projects and small projects. The question arises as to how many projects can be effectively managed at one time.

The answer, perhaps surprisingly, comes down to simple math. First, we need to make an assumption that project management typically accounts for 15% of a project’s effort hours. In other words, if a project is estimated to take 1,000 hours of effort, you should allocate 150 hours for project management. Some companies allocate 10% of hours to project management, while others allocate up to 20%, but 15% is a reasonable rule of thumb.

Once we have that basic assumption, you can look at the sizes of projects you need to manage. You apply your project management percentage and then you should be able to determine how the number of projects that one project manager can manage.

The best way to envision this is to look at some examples.

Project A, 12,000 hours of effort, one year duration

The project management time is calculated at 1,800 hours (12,000 * .15). The 1800 hours represents the typical amount of hours a person will work in one year. Since the project is also one year, there is a need for a full-time project manager. The project manager probably cannot manage any other projects since this one will absorb all of his time.

Project B, 6,000 hours, one year duration

In this case, you will need 900 hours of project management time (6,000 * .15). Since the project is spread over year, the project will need less than 20 hours of project management time per week. Therefore, it is possible for a project manager to manage two projects of this size over a one-year timeframe.

Project C, 1,000 hours, three months, 1000 hours, 150 hours of project management
Project D, 2,000 hours, eight months, 2000 hours, 300 hours of project management
Project E, 500 hours, two months, 500 hours, 75 hours of project management

In this case, Project C will need 12+ hours per week (for 12 weeks), Project D will need 8+ hours per week (for 35 weeks) and Project E will need 12+ hours per week (for 8 weeks). One project manager could manage all three projects since the total project management effort is around 32 hours per week.

Project F, 20,000 hours, one year

In this case, the project needs 3,000 hours of project management time (20,000 * .15). This represents more hours than the project manager can work in a year. This would be a reason to use a project administrator or team leaders to take over some aspects of project management. For example, a project administrator can help update the schedule, consolidate status reports, schedule meetings, and do other administrative tasks to help the project manager.

Of course, the project management time does not occur in a straight average number of hours per week. There will be some peaks and valleys of time requirements on each project. However, this is the overall model you would use to determine whether a project manager has too many, too few, or just the right number of projects to manage. 

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