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Sounds like a riddle. Many project managers wonder how many projects can be effectively managed at one time. The answer, perhaps surprisingly, starts with some simple math. First, we 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 can calculate the total number of project management hours and the period of time when the hours are spread. 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). Since the project is one year, there is a need for a full-time project manager for the year.
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.
Next we can get a little more sophisticated. As you know, 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. For example, the planning process needs a lot of project management time. A project manager could be full-time during planning and then require fewer project management hours as the project progresses. This could allow the project manager to start planning another project after the first project stabilizes. However, this is the overall staffing model you would use to determine whether a project manager has too many, too few, or just the right number of projects to manage.