What is the difference between duration, work, effort, hours, and man-days?

I come from the Microsoft Project world where schedules are built using duration and work. However, ever so often team members refer to effort, hours, or my personal pet peeve “man-days”. What are all of these and how do they compare?

My nonprofessional definitions are summarized as follows, with examples below:

  • Duration – the amount of time it takes to complete a task. Measured in days, from task start to task end. Can also be referred to as calendar time.
  • Work – the amount of hours it takes to complete a task. Measured in hours, from task start to task end.
  • Effort – the same as work if you’re talking about hours. Technically, effort is a % allocation of your “focus” on a task.
  • Hours – the same as work.
  • Man-days – the same as work, but expressed in days instead of hours.

To illustrate, we will use a simple example: We need to build a wall.

Example 1: Duration

The wall will take one builder 10 working days to build. In Microsoft Project, this would be represented as follows:

  • Duration is 10 days
  • Work is 80 hours (Assuming the builder works 8 hours a day, that’s 10 x 8 = 80 hours)
  • Effort is 80 hours
  • Hours is 80 hours
  • Man-days is 10 days. Be careful! Man-days is not the same as duration. See the next example.

Example 2: Man-days

The same wall will take two builders 5 working days to build.

  • Duration is 5 days
  • Work is still 80 hours (2 builders, each working 8 hours a day for 5 days)
  • Effort is 80 hours
  • Hours is 80 hours
  • Man-days is 10 days

Example 3:

We have two builders, but the client will only allow us to work for 4 hours in the mornings. Thereafter, we need to leave the building site. The same wall will take the two builders 10 working days to build.

  • Duration is 10 days
  • Work is still 80 hours (2 builders, each working 4 hours a day for 10 days)
  • Effort is 80 hours
  • Hours is 80 hours
  • Man-days is 10 days

In Summary:

When team members start using non-standard terminology, make sure that you understand exactly what they mean. When quoting customers on a time and materials basis, work is the only reliable source in the examples above, work remained at 80 hours regardless of how the work was resourced. Wherever possible, I always refer to Duration and Work. These are two “standards” that most other Microsoft Project users will be familiar with. Leave a comment and let me know if you found this useful.

Published by


Shaun lives and works in Johannesburg, South Africa, as an experienced PMP certified project manager with over 21 years experience in the Microsoft IT field. Shaun is passionate about project management, enterprise content management, personal productivity, patisserie, fine dining at home, Alfa’s and computer games!

18 thoughts on “What is the difference between duration, work, effort, hours, and man-days?”

    1. I can’t get #2 or #3 to work in my Project 2007 file. When I type in 80 hours, MS Project 2007 automatically changes my duration to 10 days, even though it should be 5 days, two people. Even if I have two resources it seems to always translate hours to days between these fields. What am I missing? I am trying to apply your concept to an MS project file. Thanks for posting!

      1. Thanks for bringing this to my attention, and for the feedback! Add a column called “Type” to your view. There are 3 different task types – Fixed Units, Fixed Work, and Fixed Duration – and each effect the scheduling engine differently. I’ll do another post for us shortly to explain the different task types.

    1. Yes, you are technically 100% correct. Effort is a % allocation, however when a manager approaches me and asks “How much effort to deliver this task”, he is not expecting me to answer with “it will be 100% effort”, instead the expectation is the number of hours to deliver the task. Thanks for the feedback, I’ll update the post to make this distinction clear!

  1. I am having trouble wrapping my mind around this. I just started a new job and they follow a similar format above, regarding Duration and Work.

    My question is, is the definition of PMP duration different than MProject’s definition or have I’ve misunderstood something?

    Basically, the definitions above have Duration and Work being equivelent, if they are equal they should always be equal, but in one example u get different outputs.

    If we follow PMP, MSproject’s duration field should really be schedule and the work field should really be duration?

    1. Yes, Microsoft Project implementation of duration is aligned with PMI’s PMBOK definition.

      In the example below, work is expressed in hours and duration in days. So, if 1 hour of work is needed each day for 5 days, there is a total of 5 hours of work needed, but also 5 days in duration. The reason it is 5 days duration is that you still have to wait 5 days before the work is complete.

      The PMBOK 5th Edition defines duration as “The total number of work periods (not including holidays or other nonworking periods) required to complete a schedule activity or work breakdown structure component. Usually expressed as workdays or workweeks.”. See http://www.pmi.org/PMBOK-Guide-and-Standards/PMI-lexicon.aspx#D

      Microsoft Project 2010 defines duration as “The Duration field is the total span of active working time for a task. This is generally the amount of working time from the start to the finish of a task.”. See http://office.microsoft.com/en-za/project-help/duration-task-field-HP045305001.aspx?CTT=5&origin=HP045305003

      Max Wideman PM Glossary defines duration as “The length of time needed to complete an activity.” It goes on further to explain “The planned or actual elapsed time between two events, e.g. between the start and finish of an activity, between two milestones or the whole project. Duration may be measured in units of calendar time, or project calendar time. It can be misleading to measure it in days worked on an activity since calendar and working time may pass with no production. It is totally wrong to measure duration in man-hours or man-days which are
      units of work, not time”. See http://www.maxwideman.com/pmglossary/PMG_D04.htm

      Hope this helps you!

  2. Hi Shaun,

    My apologies in a delayed response, I was out with the flu.

    Yes, thank you. It does make sense and is helpful to see how others define duration as well. This method is certainly how my coworkers are using the system. I was taught a slightly different way in my project management program. Thnx!

  3. Hello Shaun,

    I am studying Project Management at a local Polytechnic in Singapore. I am supposed to find the optimum project duration and cost and I have some trouble understanding the assignment.
    The assignment specified the ‘effort in Man-Days’ and ‘Material Cost’.
    What does those 2 terminologies refer to?

    L = Skilled Labour E = Engineer

    Name Effort in Man-Days Material Cost
    Activity1 L (532.00d), E (5.25d) $11,500.00

    Is this understanding correct:
    1 Labour will finish Activity1 in 532 days
    1 Engineer will finish Activity1 in 5.25 days

    Lastly how do I put this resources on Microsoft project? Sorry for troubling you!

  4. I think concepts as Effort or Man-Days are not well defined.

    Case #2 and #3 couldn’t have same Work and same Effort with different Duration if you understand Effort as in common Project Management concepts (W=D*E)

    Isn’t It?

  5. I’m not convinced that scheduling terms that are often used are sufficiently intuitive. I propose the following terms for the three attributes:
    Elapsed Time = Hours of Work / Resources Allocated.

  6. Dear Shaun,
    Is this Example 4 correct?
    Requirement: Work is 80 hours and 1 builder can work only for 4 hours.

    •Work is still 80 hours (1 builders, working 4 hours a day for 20 days)
    •Duration will be 20 days
    •Effort is 80 hours
    •Hours is 80 hours
    •Man-days is 20 days

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.