Project Effort vs Duration vs Elapsed Time: Are They Different Or Same?

project duration and effort

What is the difference between project effort and duration? Do work and effort mean the same thing? What’s the distinction between project duration and elapsed time?

I have written this article to answer these kind of questions. You find difference between and explanation of project effort vs duration vs elapsed time in this article.

Project Effort, Duration, and Elapsed Time

There is a lot of confusion about different time management terms. I am always asked questions about project duration, effort and elapsed time during my training classes.

Let’s take an example. What would you understand if I say, “Activity Alpha would need 3 days for completion”.

This statement can be confusing without the proper context. ‘Days’ could mean one person working for 3 days. Or, it could mean can entire team working for 3 days. It can also mean 3 days for completion including non-working time and holidays.

I think the main cause of this confusion is our day to day conversations. We use time units like days & weeks and time management terms like effort & duration interchangeably in our daily conversations.

Definitions & Meaning

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

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

Elapsed time is the total amount of time that passes between start of an activity and end of the activity.

These project managemeent terms have completely different meaning. One term should not be used in place of the other. Let us explore these terms further with the help of an example.

Project Effort

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

Again, a task could mean an entire project or a WBS component or an activity. Effort is sometimes expressed in hours, days, or weeks but it is better to use person hours, person days or person weeks 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.

Project Duration

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

A 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, or weeks but it is better to express it 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.

Elapsed Time

Elapsed time is the total calendar time needed to complete a task. It includes weekends, holidays, vacations and breaks.

Again, a task could mean an entire project or a WBS component or an activity. Elapsed time is usually expressed in hours, days, or weeks, which is appropriate.

Example of Project Duration, Effort, and Elapsed Time

Let us consider a small task that involves painting one large wall.

Assumptions & Estimates

  • 1 work day = 8 work hours. It means that painter(s) will work 8 hours per Day.
  • The painting task has a Duration Estimate of 4 work days with only 1 painter working.
  • There is no scarcity of painters. There are enough painters available to do the task.
  • All painters have equal productivity. The amount and quality of the work is same for each painter.
  • The task will start on Friday.
  • Saturday and Sunday are holidays.

Duration

  • If 1 painter works, the duration of the task would be 4 work days or 32 work hours.
  • If 2 Painters work, the duration of the task would be 2 work days or 16 work hours.
  • If 4 painters work, the duration of the task would be 1 work days or 8 work hours.

Elapsed Time

  • If 1 painter works, the task will start on Friday and finish on Wednesday. The elapsed time would be 6 days.
  • If 2 Painters work, the task will start on Friday and finish on Monday. The elapsed time would be 4 days.
  • If 4 painters work, the task will start and finish on Friday. The elapsed time would be 1 days.

Effort

  • If 1 painter works, the effort for the task would be 4 person days or 32 person hours.
  • If 2 painters work, the effort for the task will remain same – 4 person days or 32 person hours.
  • If 4 painters work, the effort for the task will still be same – 4 person days or 32 person hours.

Work

Work is synonymous with effort. MS Project uses the term ‘work’ for doing calculations related to effort.

Project Effort and Duration Formula

Let us continue from the above example. The relationship between project effort and duration can be best expressed by the following formula:

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

This formula will not work in all cases but it gives a fair idea of the relationship. This formula will work only if:

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

For example, the formula would not work while developing a piece of software code as one developer cannot work on a piece of code without having dependency on the other developer.

Over To You

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

PMP Exam Formulas

I have also compiled a PMP Formulas Cheat Sheet. It contains 45 formulas and 57 abbrviations. It will help you in your exam prep. You can freely download the PMP Formulas Sheet for your studies. It is the best and most comprehensive cheat sheet based on the PMBOK Guide 6th edition.

If you are looking beyond a cheat sheet, then I would suggest you to buy detailed PMP Exam Formula Study Guide by Cornelius Fichtner. It contains detailed explanations of all the formulas along with examples and 105 practice questions.

Disclosure: This article contains affiliate links - it means that, if you buy from any of these links, then I will receive a small commission that would help me in maintaining this blog for free. However, for you, there is no extra cost. I recommend only those products that I believe will definitely help the certification aspirants.

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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