Monday, January 14, 2008

Distributing Task Hours

Lately, I have been seeing project plans that attempt to distribute work between resources by using units allocation. But percent resource allocation is not the same as percent work performed. Allocating a resource at 50% units only means that he will work on the task half-time, not that he will do half the work!

For example, let's say that we have a 16 hour task (2 days duration, assuming an 8 hour day), and we want a resource named Able to perform the task:

To start, let's put Able on the task full-time:


Wrong way to distribute task hours

Now, because we want Able to perform only 25% of the task, we do the wrong thing and adjust his units to 25%:


As you can see, the work effort stayed the same, meaning Able is still performing 100% of the work. Only the duration changed, so by changing the units, it just takes longer to get the task done. This plan does not show that Able will perform only 25% of the work. It only shows that Able will work on the task 25% of his available time.

Right way to distribute task hours

Now suppose we want resource Able to perform 25% of the task, while resource Baker performs 75%. Remember this means percent of the actual work, not percent resource allocation.

This is what we're after:


The duration will be 1.5 days because Able works 4 hours (25% of 16) to complete his part, while Baker works 12 hours (75% of 16). Both resources are allocated to the task 100%, so Baker's 12 hours equates to 1.5 8-hour days.

How to do it in MS Project

Go to the task usage view (either entry view or usage view).

You can distribute the task hours however you want by entering a value in the work column. Make sure you do the math correctly so the duration is the same when you're done making changes.

Return back to the task sheet or Gantt chart view. The resources are still allocated at 100%, and the duration is still the same.

Advanced usage

Now try adjusting resource Baker's units to 50% on this task, so he is allocated at 50% to his 75% of the task.

You should see the task duration increase to 3 days. Why? Baker still has 12 hours work to do, but can only spend 50% of his available time on it. So the task duration increased to 3 days, but the work stayed the same at 12 hours. Since 12 hours of work take 1.5 8-hour days, Baker should take 3 days to complete 12 hours of work at 50% allocation.

You might also want to consider changing the task type to fixed units.


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