Page 147 - Project+

Determining task durations is the next step in constructing the project schedule.

Duration estimating can be as easy as an expert giving you an educated estimate based
on their experience, or it can be a complex process involving techniques and
calculations to develop estimates—albeit most of these estimates are still based on
expert opinions.

Before explaining some of the techniques you can use to complete your task duration
estimates, let’s make sure we have a common understanding of activity duration.

Defining Duration

When you are estimating duration, you need to make sure that you are looking at the
total elapsed time to complete the activity. For example, let’s say you have a task that is
estimated to take five days to complete based on an eight-hour workday. You have one
full-time resource assigned to this task, but they have only four hours a day to work on
it. That means the actual duration estimate for this task is 10 days.

You also need to be aware of the difference between workdays and calendar days. If
your workweek is Monday through Friday and you have a four-day task starting on
Thursday, the duration for that task will be six calendar days because no work will be
done on Saturday and Sunday. Figure 5.3 illustrates this situation. The same concept
applies to holidays or vacation time.

FIGURE 5.3 A four-day task separated by the weekend

Make certain that everyone who is providing estimates is in agreement up
front as to whether they will be provided in workdays or calendar days. We
recommend using workday duration estimates. Most project management
software packages allow you to establish a calendar that accounts for nonworkdays

and will exclude these days when computing duration.

Now that we have a common understanding of duration, I’ll discuss the different
techniques used to create duration estimates.

Estimating Techniques

You can use several techniques to determine task duration estimates. You’ll look at
three of the most common methods.

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