Microsoft Project 2013: The Missing Manual

Estimating Task Work and Duration

You’ll never predict project duration with total accuracy. However, estimating work time and task duration as closely as you can is the goal, because both high and low estimates can cause problems. Overestimate how long your project will take, and the project might get squelched before it begins. Underestimate, and you might run into disappointment, extensions, and financial consequences. This section explains the difference between work and duration and then describes several methods for obtaining estimates.

Understanding Work and Duration

In Project, work and duration are both ways of measuring time, but each term has a specific meaning:

• Work. The number of person-hours (or equipment-hours) a task requires. For example, setting up a website may take you (that is, one person) 40 hours.

• Duration. The span of work time from the start of a task to the finish. Duration varies according to how many resources (people or equipment) you use, and when those resources are available. If you have other things to do and can’t spend more than 4 hours each day on the website, you may need 10 workdays for that 40-hour task. On the other hand, if you convince three colleagues to help (and they share your skills), the duration decreases to a little more than one workday, but the four of you still devote 40 hours of work to the task.

Whether you estimate work, duration, or both depends on whether you know how many people are available to work on tasks. If you don’t know ...