# What methods are there to figure out how adding people to the project will reduce the amount of time needed?

I've been asked to estimate how long it will take for a big project to get done, and I was able to break it up into small tasks and come up with an estimate for one person do it.

However, I'm now being asked to figure out how many people will be needed to finish the task and how long it will take.

What methods are there to figure out how adding people to the project will reduce the amount of time needed?

I know that the more people you add the more time that gets spent on communication and that the division is not linear. In addition, some team members will block others, some work can be done in parallel and some can't.

This is my first project with these teams and of this scope, so I don't have past experience to work with.

• Is this a software project? If so, then are you using agile? May 17, 2017 at 9:37
• @SahanDeSilva It is a software project. We are using a mix of agile and waterfall. At the current stage (high-level planning) it's waterfall but when we start development each team will use agile processes.
– avi
May 17, 2017 at 10:15
• So, you've not worked with these teams personally, that doesn't mean there isn't historic data to use. Do everything you can to find it and use it. Then quickly discard it and update your estimates based on data from this project. May 17, 2017 at 16:33
• If you breakdown the requirement into a proper WBS, then you can assign each task to a team member, right? So then you can calculate the total time, add an additional amount of time as a contingency reserve and provide the total time estimation. (You can also go for 3 point estimation - PERT) I'm not adding this as an answer because I'm not sure which path you need to work on. May 18, 2017 at 3:52
• PERT is a really good first step.
– avi
May 18, 2017 at 7:36

Your benchmark formula is Duration (in days) = Work (in hours) / Utilization (workers). This assumes perfect resource elasticity. There're few tasks with perfect resource elasticity.

If you have a reasonable estimate for the work based on one worker, then use this formula to calculate the same estimate using additional workers. This will establish your floor.

I am also assuming you established your one worker estimate resulting in a range, i.e., best, worst, most likely. If you did not, then you need to do this.

Since tasks are rarely perfectly elastic, your challenge is to arrive at a multi-worker estimate where you have little to no experience. Since you have the floor as established above, you need to arrive at how much "fat" you need to put into this estimate since you are carrying a lot of risk.

You need to consult as many SMEs in this work area as you can find to get an idea of what the "engineering estimates" look like, knowing that this type of estimation has significant validity issues secondary to human biases. You need to research historical data on similar projects if you can find them and use them where you can, understanding that this too has some validity issues such as how accurate is the data in the first place. If you are able to uncover any parametrics with the tasks, use them where you can; however, in knowledge-type work, these don't really exist with any degree of high reliability and validity.