One of the most confusing parts of Microsoft Project is the Task Type. The relationship between Activity Duration and Resource Assignment is defined by this field value. This article explains in detail the use of each task type and it’s effect on resource assignment calculations.

MS Project allows 3 parameters:

- The task Duration
- The number of hours required to complete a task (Work)
- The Units per time period (the rate of doing the work, or the number of resources required per time period)

The relationship of these three parameters can be described by the following formula:

Duration x Units = Work

For example, if there was a 2-day activity with a resource assigned at 8 hours per day, the Duration will be 2 x 8 = 16 hours. If two people will work on the task the units assigned will be 200% (2 x 100%) and the resultant work calculation will be 2 x 16 hours = 32 hours.

MS Project allows three task types:

- Fixed Duration: the duration is fixed and remains constant and a change to Duration changes the Work
- Fixed Units: the units per time is fixed and remains constant and a change to Units will alter the Duration
- Fixed Work: the work (hours) are fixed and remain constant if either the Duration or Units are changed

You could picture the above task types in a triangle:

If you fix one side of the triangle and manipulate another, the remaining side will be calculated. For example, if you fix the Units, and enter the Duration manually, the Work will be calculated.

If you’re keen to try this formula out, add three tasks each with a different task type. Add a single resource to each task and manipulate the various parameters.