Manmonth

Man-month is a unit of work representing the amount of effort that one person can complete in one month of full-time work. It is commonly used in project estimation, planning, and staffing to express required effort independent of calendar duration.

The total amount of work for a project can be expressed as the sum of man-months, calculated by multiplying the number of workers by the number of months they will work on the project. For example, three developers working for two months provide six man-months of effort. Because the number of hours in a month varies by country and working arrangement, one man-month is only an approximate measure.

A commonly cited range is about 160 to 173 hours, depending on whether a standard month is taken as four weeks, or as roughly 52 weeks divided over 12 months. In practice, man-months are used as an abstraction for planning; they do not guarantee calendar time, since parallel work, productivity differences, onboarding, vacations, and meetings can extend or compress real durations.

The term has faced criticism for its gendered wording; many organizations prefer person-month or staff-month. In modern project management, alternatives include unitless effort estimates, or expressing requirements directly in person-hours, person-days, or feature points. Despite limitations, the man-month remains a widely used shorthand in fields such as software engineering, research, and engineering for expressing project effort and resource needs.