Duration is the length of working time between the start and finish of a task. Project bases the calculation of a task's duration on the amount of work and the amount of resource units assigned to it. The working time for a task is defined by the project calendar, resource calendar, task calendar, or any custom calendars you set for a project.
Work is the amount of effort, measured in time units (like hours or days), that a resource needs to complete the task. The total work for a task is the sum of all those time units, no matter how many resources are assigned to the task.
Resource Units indicate how much of a resource's available time, according to the resource calendar, is being used to work on a particular task. Resources are the people, equipment, or other materials that are applied to completing a task. In a project schedule, resource effort is expressed as assignment units or sometimes just as units.
Before you assign a resource to a project task, the task has duration but has no work associated with it. Why not? Because work represents the amount of effort a resource or resources will spend to complete the task.
To get the most out of scheduling in Project, you need to understand and effectively use all three parts of the scheduling formula: Duration = Work ÷ Resource Units.
When you assign resources to a task, based upon the scheduling formula, Project calculates the task's effect on the schedule by using the values assigned to the Work, Duration, and Resource Units associated with the task.
- Note For this lesson, we only refer to "people" resources, also called work resources, not material resources such as lumber, paint, concrete, or video tape.
These three elements of the scheduling formula also correspond to task types, a setting which you can apply to individual tasks, allowing you to adjust that task type's influence on the schedule.