Before you can estimate duration, you must understand the
effort hours associated with your project. For example, what is the duration of
an activity that takes 40 effort hours? The duration could be less than a week
if multiple people are involved, and it would take longer than a week if only a
part-time resource is involved.

For the sake of discussion, however, let’s say that one
person is assigned to this 40-hour activity. As the project manager, should you
estimate that the duration of the activity is one calendar week? Maybe that
would not be the best choice.

There are a number of factors that come up during the day
that keep us from being fully productive. For example, let’s say you work
8:00-5:00 with a one-hour lunch. Is it really the case that you are at your
desk at 8:00 and you are 100% productive? Do you then maintain a 100% peak
performance until 12:00 and then immediately shut down and go to lunch?
Likewise are you always at peak performance from 1:00 until the end of the day?

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None of us can work at that pace all day. These normal peaks
and valleys of our day keep us from being 100% productive for the full eight

Socializing is another cause for this productivity drop, but
this isn’t a bad thing. Social interaction helps with the teamwork and comradery that are a big part of what makes up a
high-performing team. Of course, we all know people that take the socializing
to an extreme, but some socializing is healthy and necessary.

Other factors that interrupt our eight hours of work time
include going to the bathroom, walking to and from meetings, phone calls and
the start-up time required when you multitask from one activity to another.

A generally accepted rule of thumb for average productive
hours per day for employees is 6.5, based on an eight-hour day. This does not
mean that in any one day a person may not be productive for a longer time.
However, it does factor in a person’s productive hours per day over time.

You should also take a productivity factor into account for
your contract resources. They’re still going to socialize a little and they
still need to go to the bathroom. However, you don’t expect that contract
people will have the same level of non-productive time as employees. A good
rule of thumb for a contract resource is 7 to 7.25 productive hours per day. (Of
course, you still need to pay them for eight hours per day.)

This productivity factor can be used to determine the
duration of activities in your workplan. (There is a
place to plug in this factor in most project management tools.) For example,
let’s say you have an 80 hour activity. If one employee is applied full time,
it may take him a little over twelve days (80 / 6.5 productive hours per day)
to complete the work. If a contract resource is allocated full time to this
same activity, the activity duration would be eleven days (80 / 7.25 productive
hours per day). This is a more reasonable expectation of how long activities
will take to be completed, and you want your workplan
to be as realistic as possible.