What is the Difference Between Project Effort and Duration?

project duration and effort

project effort and durationI recently posted a series of articles on Project Network Diagrams. I wrote an article on Start to Start Relationship. I described the relationship using a small example. While explaining the example I wrote a statement – “The Project Team will need a total of 3 days to complete these activities”. A very senior Project Management Author & Trainer commented on my article. He said that this statement could be confusing. He said that the Days can be understood to mean either Project Effort or Duration.

I completely agree with his comment. During my training the students always ask me “what is the difference between Project Effort and Duration”. I have noticed that many people are not able to distinguish between these terms. They include senior industry professionals, Project Management practitioners and subject matter experts. In fact, I have observed that many Project Management authors have used these terms interchangeably.

In my opinion, you should first understand a Project Management term as a plain English term. Later on, you should delve deeper and understand the Project Management behind the term. In plain English:

Duration refers to the length of time or the time taken to complete a task.

Effort refers to the amount of exertion or the amount of work done to complete a task.

The terms Project Effort and Duration have completely different meaning. One term should not be used in place of the other. Let us understand Project Effort and Duration through definitions and example.

Project Management Definition & Explanation of Of Effort and Duration

Duration

Duration is the total number of work periods required to complete a Task.

The Task could mean an entire Project or a WBS Component or an Activity. Duration does not include holidays and non-working periods. Duration is usually measured & expressed in Hours, Days, and Weeks etc. But you can express Duration in Work Hours, Work Days or Work Weeks in order to avoid any confusion.

You can also look at Max Wideman’s Glossary for some other definitions of Duration.

Note: Duration is different from Elapsed Time.

Effort

Effort is the number of labor units required to complete a Task.

Again, the Task could mean an entire Project or a WBS Component or an Activity. Effort is sometimes expressed in Hours, Days, and Weeks etc. But you should use Person Hours, Person Days or Person Weeks to express Effort in order to avoid any confusion. Some Project Management authors prefer to use ‘Man’ or ‘Staff’ as prefix to express Effort e.g. Man Hours, Staff Days, Staff Weeks etc.

You can also look at Max Wideman’s Glossary for some other definitions of Effort.

Example of Project Effort and Duration

Let us consider a small task that involves Painting Walls.

Assumptions & Estimates

  • 1 Work Day = 8 Work Hours. It means that Painter(s) will work 8 Hours per Day.
  • The Task has a Duration Estimate of 4X Work Days with only 1 Painter working.
  • There are many Painters available to do the Task.
  • All Painters have equal productivity. The amount and quality of the work would be same for each Painter.

Duration

  • If 1 Painter works, the Duration of the Task would be 4X Work Days or 32X Work Hours.
  • If 2 Painters work, the Duration of the Task would be 2X Work Days or 16X Work Hours.
  • If 4 Painters work, the Duration of the Task would be 1X Work Days or 8X Work Hours.

Effort

  • If 1 Painter works, the Effort for the Task would be 4X Person Days or 32X Person Hours.
  • If 2 Painters work, the Effort for the Task would again be 4X Person Days or 32X Person Hours.
  • If 4 Painters work, the Effort for the Task would again be 4X Person Days or 32X Person Hours.

Relationship between Project Effort and Duration

Let us continue from the above example. The relationship between Project Effort and Duration can be best expressed by following formula:

(Effort) = (Duration) * (Number of Resources)

This formula will not work in many cases. But, it gives a fair idea of the relationship between Project Effort and Duration. This formula will work only if:

  • Work can be easily distributed among many Resources.
  • There is no dependency between the Resources.
  • The productivity of all Resources is considered equal.

For example, the formula would not work while developing a piece of software code.

Over To You

What units do you use to connote Project effort and Duration? Do you use any formulas? Please leave a comment.

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Praveen Malik, PMP

​Praveen Malik ​is a certified Project Management Professional (PMP®) with a rich 23+ years of experience. He is a leading Project Management Instructor, Coach and ​Advisor. He ​has successfully trained thousands of aspirants for the PM certification exams.

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Neal Reply

Regarding the example of Duration, if 1 Work Day = 8 Work Hours and 4 painters were to work 1X Work Day, then wouldn’t the answer be 32X Work Hours?

    Christi Nayar Reply

    Great topic. How much time is spent in working out is duration and how much energy is spent is effort. Thanks.

Praveen Malik, PMP Reply

Hi Neal, Duration would be 8X Work Hours and Effort would be 32X Person Hours.

    Meikey Reply

    If u jlhave 5 people who can be assigned to any task and must work full days on each activity… You have 11 activities and for activity A u have 15 person-days required…. What is the duration or how do u change the activity person days to duration when setting up a gantt chart? I am a bit confused with this person-days cause we are only given the activities (A-K) and the person-day required (A=15,B=8,C=5…)

David Kase Reply

Can effort vs duration also be used to describe a task that may only take, say, 4 hours of effort but, due to time available or waiting for replies, may take 5 days to complete? Effort = 4 hours, Duration = 5 days

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