I have a question about communication channels that is talking about person-month but I don”t understand what is a person-month. Does it mean this many persons? or this many months?

Here is the full context:

Based on statistical data in a company, communication path between two persons consumes 5% of each person’s time (during a 8-hour work day). For a project that requires 12 persons-months of development time, how many people will be needed to finish the project in four-months if (a) the democratic team structure is used and (b) the chief-programmer team structure is used. If the team consists of four persons, what is the difference in the completion time for a team using the democratic structure and a team using the chief-programmer structure?


Person-month is politically correct synonym for Man-month.

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It”s mean amount of work performed by the average worker in one month.

So, if:

project requires 12 persons-months of development timeall team members do only pure development activity (i.e. they are telepaths and they don”t need to spend time for communication with each other).


4 developers will spend 3 months for 12 persons-months project.

ProjectScopeInPersonsMonths / NumberOfDevelopers = NumberOfRequiredMonthsForProject

4 months required for 3 developers to finish 12 persons-months project.

ProjectScopeInPersonsMonths / NumberOfMonths = NumberOfRequiredDevelopersForProject

P.S. This is a wiki article about this term.

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Not to be pedantic, but the correct way to write the term would be person-month, or man-month. The distinction is that person/month implies units of people per month. This is inaccurate.

A person-month is a unit of work that”s calculated by multiplying the number of persons by the number of months they work. So a team with three developers working on a task for two months has expended 6 person-months of labor. A person-month is equivalent to hours of labor (160 hours is a common value), but work is often expressed in person-month units because it’s easier to get a feel for how many people might be needed to finish a body of work in a fixed time, or conversely how long it might take a fixed group of people to finish a task.

However, the term man-month been broadly criticized when used as a predictive metric, most famously by The Mythical Man-Month, which makes a strong argument that man-months are not fungible in this naïve manner. That said, it’s still a useful unit of work.

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In calculus terms, a person month is calculated by taking the integral of staffing as a function of time between two dates.

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