A colleague and I were discussing how Microsoft Project calculates duration, work, and resource utilization. My colleague was managing an outsourced project under a time and materials contract and wanted to schedule a four-hour task over three days. He had a few challenges trying to schedule the task in Microsoft Project until we discussed the importance of task types and the Duration X Units = Work equation.
Microsoft Project schedules tasks based on three variables: duration, units (or resources), and work. You get to choose two of these variables, and Microsoft Project calculates the third. Project managers run into a scheduling circle when they try to hold all three of these variables fixed. Just like the scope, cost, and time project triangle, if you change one variable, the others adjust as well.
In my colleague's scenario, the project manager has three days to complete four hours of work. Since the project is outsourced to a vendor, and the project manager doesn't have direct control of the resource, a fixed duration task type is recommended. The project manager doesn't care when the work gets done, as long as it's in the three day estimate. By setting the task to use a fixed duration task type, the number of hours and resources can fluctuate, and the three day duration will remain constant.
In actual practice using a time and materials contract, the project manager would care about the number of hours spent from a budget perspective. From a schedule perspective, the project manager is still expecting a three day fixed duration for the task.Using the Duration X Units = Work formula, the project manager will enter duration and work into Microsoft Project and let the tool calculate resources.
To create a four-hour task using a three day fixed duration, follow these steps:
- Insert the Type and Work fields into the Gantt Chart view.
- Enter the task name.
- Change the Type field to Fixed Duration.
- Enter 3 days in the Duration column.
- Enter 4 hrs in the Work column.
- Assign a resource.
- Microsoft Project will calculate the 17% utilization.
Figure A: three-day duration with four hours of work
In the Task B example, a Fixed Work task could be entered with a resource assigned 100%, and the resulting duration would be 0.5 days. Since the requirement is to complete the task within three days, the fixed duration task is recommended.
For internal projects with internal resource costs, I prefer to build fixed duration tasks using 100% allocated resources and let Microsoft Project calculate the work. For external projects that use different contract types, the mix of task types will depend upon the work and the level of tracking required in your project schedule.
To learn more about the different task types, read my Microsoft Project tutorial, Use Fixed Duration, Fixed Work and Fixed Unit Type Fields.