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.