Estimation of the work volume and time for each task can be done in a variety of ways: according to work or time—depending on the type of task.
Variable Duration Tasks are tasks for which the duration depends on the number and type of resources allocated for their completion. Estimating this type of task should be done based on the amount of work required. Once resources are assigned to the task, its duration can be derived using the following formula:
Work / Units (number of resources) = Duration
For example: Painting an apartment requires forty hours of work by an experienced painter. The duration of the task depends on the number of painters assigned to it. One experienced painter can paint the apartment in five working days. Two experienced painters can paint the apartment in two and a half days. An experienced painter working part-time or an inexperienced painter can paint the apartment in ten working days.
Fixed Duration Tasks are tasks for which duration does not depend on the number or type of resources assigned for their completion, however, the cost of the task does. Estimating this type of task would be done based on projected task duration. Once resources are assigned to the task, its total cost can be calculated using the following formula:
Duration x Units (number of resources) = Work
For example: It takes a fixed amount of time to wash a car in an automatic car wash. However, cleaning the car’s interior and drying the car are tasks that can be done by one or more workers. In this case, the sum total of the work and the cost of the task will change depending on how many workers are assigned to it.
Remember that the estimated task duration is a net time estimate and not its actual duration. To calculate its actual duration, the work plan must also take into consideration weekends, holidays, vacations, and any other days during which no work will be performed. It is also important to take into account the fact that most human resources will not dedicate 100% of their time to a single task. There will always be distractions in the background—meetings, support activities for previous tasks, and so on. Therefore, it is recommended that human resources not be assigned based on maximum possible efficiency for each task. Rather, time must also be allocated to support activities that do not appear in the project’s work plan.
Common ways for estimating task work or duration: