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Estimating a project with many unknowns

We have an estimation about our project time by man/hour. Now we want to know how much our project will take if we have more than one programmer? Do you have any idea how to estimate this? Any formula?

Community
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Saeed Salmani
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    [Division](https://secure.wikimedia.org/wikipedia/en/wiki/Division_%28mathematics%29)? – President James K. Polk Mar 05 '11 at 14:13
  • Please search here and http://programmers.stackexchange.com/questions for all of the questions on estimation. After reading all those questions, please **update** yours to not duplicate all the other identical questions. For example: http://stackoverflow.com/questions/3972640/estimating-a-project-with-many-unknowns is identical to this question. – S.Lott Mar 05 '11 at 14:14
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    At least the time will not decrease ten times if you assign 10 coders. Some time will go to interaction, team works etc – simon Mar 05 '11 at 14:15
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    Multiply by 1.5 if they don't like eachothers programming style – Pleun Mar 05 '11 at 14:15
  • When a programmer estimates time, multiply by 4 and use the next larger unit to get a realistic timeframe. 1 hour -> 4 days. 1 week -> 4 months. – Erik Mar 05 '11 at 14:15
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    Have a look at Brook's Law: http://en.wikipedia.org/wiki/Brooks%27s_law – Bernd Elkemann Mar 05 '11 at 14:17
  • You can also search on the [Project Management](http://pm.stackexchange.com/) site for answers to similar questions. – Bill the Lizard Mar 05 '11 at 14:28

1 Answers1

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If you have the estimation in man-hour, you just have to divide that number by the number of people working on it to get the number of hours it will require.

So a 6 man-hour project will take 6/1 = 6 hours with 1 programmer, 6/2 = 3 hours with 2 programmers.

I think wikipedia has a good article on this topic : see Here

EDIT: ok since people tends to make me believe this is more than a "use of the man-hour system" question, here is some more tips :

To manage a project with more accuracy than the system you have multiples tools that can help your. Many of them are included in project management systems.

First of all you need to identify sub units of the development. Then you'll be able to make a GANTT chart with dependencies that will build a structure in your project.

By doing so, and assigning people to sub units, you can by the mean of man-hour system estimate the time required for this particular unit. Then the different constrains put up by dependencies, vacation days (and so on), will give you the estimate date of end of works.

GANTT also allow you to work backwards: setting up constraint on end of project and using the dependencies constraints to compute the beginning date of your project.

Pieces of software that will help you do that are (non exhaustively) MS Project, Gantt project (open source) and surely a lot more.

You can also look on different tools use by project managers : PERT chart, activity diagram and many other I do not use and/or know about.

I hope this provides more useful help than the previous edit.

M'vy
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  • Read the [mythical man month](http://www.amazon.com/Mythical-Man-Month-Software-Engineering-Anniversary/dp/0201835959) for why this is not so. Each person you add, adds another person to communicate with. Humans do not share brains like processes on a computer share RAM :) – Konerak Mar 05 '11 at 14:19
  • Comment: Man-hour does not care about pauses etc... it's pure work. – M'vy Mar 05 '11 at 14:19
  • If it takes 1 person 8 hours to build a wall, it does not take 8*60 persons just one minute to build the same wall... – Konerak Mar 05 '11 at 14:20
  • Of course, it's just an estimation, and the man-hour system does not allow you to be more precise. You can go on some project management tools to get more accurate. – M'vy Mar 05 '11 at 14:22
  • 9 women cannot get a baby in one month... – Pleun Mar 05 '11 at 21:12
  • Thank you very much. I think I get it (Please refer to further edits). – M'vy Mar 05 '11 at 21:19