Improve Task Estimates, Multiply by Pi

Trouble with poor task estimation?  Introducing the three-point estimating technique.  This might help.

Te = (To + 4Tm + Tp) / 6

Here’s the problem: engineers are never good at estimating task durations.  Not even close.  When asked how long their tasks will take, they usually just say, “They’ll be done when they’re done!”  As a project manager, you have to coerce an estimate out of them.  And then multiple by Pi for the real number.  But there may be a better way.  Read on for a possible solution.


                It’ll take about two and a half months.

                Multiple by Pi

                Result: eight months

First off, Engineers just don’t like estimating time.  They have technical issues to deal with, and are not practiced in the arts of time estimation.  They feel uncomfortable in fuzzy areas like this because they don’t spend any time thinking about such things.  The traffic in mathematical and logical conundrums, not project scheduling.  You might just as well ask them how much their tasks will cost, or how much the company will make from the product, once marketed.  It’s just not something they spend any time considering.  That means you have to take their task estimates with a grain of salt, or perhaps with a more scientific calculation.

What could be more scientific than multiplying them by Pi?  🙂

The three-point estimate technique below first appeared with PERT (Program Evaluation and Review Technique).  It has some merit when dealing with task durations, and might be more accurate than multiplying engineer estimates by some arbitrary number.

Start by taking this three-point estimate below from the engineer for each task.  You must get them to tell you the most likely duration for each task, which they will understate by a longshot… then you must try for an optimistic estimate, which they will assert is the same as the first estimate… then finally you have to get them to spit out a pessimistic duration, at which point they will argue is also the same as the first two, and that you are stupid for asking… now go away!  But if you can get these three numbers, you can plug them into the three-point estimate calculation below.

  • 1. Tm – Most Likely estimate (example: 6 months)
  • 2. To – Optimistic estimate (example: 4 months)
  • 3. Tp – Pessimistic estimate (example: 12 months)

With these three estimates, you can run a calculation to find the mean estimate.  (Find this calculation on page 150 of the PMBOK.)

                Te = (To + 4Tm + Tp) / 6

                Example: (4 + 4(6) + 12) / 6 = 8 months

The results are a good prediction of human estimations, assuming that most people under-judge the duration of most tasks.  They simply forget or don’t consider all the possible details in executing their assigned tasks.  This calculation makes up for that lack of detail.

Hope it works for you!