Man hour
A man-hour or person-hour is the amount of work
Manual labour
Manual labour , manual or manual work is physical work done by people, most especially in contrast to that done by machines, and also to that done by working animals...

 performed by an average worker in one hour. It is used in written "estimates" for estimation of the total amount of uninterrupted labour required to perform a task. For example, researching and writing a college paper might require twenty man-hours. Preparing a family banquet from scratch might require ten man-hours.

Man-hours do not take account of the breaks that people generally require from work, e.g. for rest, eating, and other bodily functions. They only count pure labour. Managers count the man-hours and add break time to estimate the amount of time a task will actually take to complete. Thus, while one college course's written paper might require twenty man-hours to carry out, it almost certainly will not get done in twenty consecutive hours. Its progress will be interrupted by work for other courses, meals, sleep, and other distractions.

Real-world applications

The advantage of the man-hour concept is that it can be used to estimate the impact of staff changes on the amount of time required for a task. This is done by dividing
Division (mathematics)
right|thumb|200px|20 \div 4=5In mathematics, especially in elementary arithmetic, division is an arithmetic operation.Specifically, if c times b equals a, written:c \times b = a\,...

 the number of man-hours by the number of workers available.

This is, of course, appropriate to certain types of activities. It is of most use when considering 'piece-work', where the activity being managed consists of discrete activities having simple dependencies, and where other factors can be neglected. So, adding another man to a packaging team will increase the output of that team in a predictable manner. In transport industry, this concept is superseded by passenger-mile and tonne-mile for better costing accuracy.

In reality, other factors intervene to reduce the simplicity of this model. If some elements of the task have a natural timespan, adding more staff will have a reduced effect: although having two chefs will double the speed of some elements of food preparation, they roast a chicken no faster than one chef. Some tasks also have a natural number of staff associated with them: the time to chop the vegetables will be halved with the addition of the second chef, but the time to carve the chicken will remain the same.

Another example is the old adage, "Just because a woman can make a baby in 9 months, it does not follow that 9 women can make a baby in one month." This adage is oft cited in systems development to try and justify the belief that adding more staff to a project does not guarantee it will get done quicker.

Another problem with this model, as Fred Brooks noted, is that organization, training, and co-ordination activities could more than outweigh the potential benefits of adding extra staff to work on a task, especially if considered only over a shorter time period.

Similar units

The similar concept of a man-day, man-week, man-month, or man-year is used on very large project
A project in business and science is typically defined as a collaborative enterprise, frequently involving research or design, that is carefully planned to achieve a particular aim. Projects can be further defined as temporary rather than permanent social systems that are constituted by teams...

s. It is the amount of work performed by an average worker during one day, week, month, or year, respectively. The number of hours worked by an individual during a year varies greatly according to cultural
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

Norm (sociology)
Social norms are the accepted behaviors within a society or group. This sociological and social psychological term has been defined as "the rules that a group uses for appropriate and inappropriate values, beliefs, attitudes and behaviors. These rules may be explicit or implicit...

(s) and economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...

. The average annual hours actually worked per person in employment as reported by OECD countries in 2007, for example, ranged from a minimum of 1389 hours (Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

) to a maximum of 2316 hours (South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...


See also

  • Henry Gantt
    Henry Gantt
    Henry Laurence Gantt, A.B., M.E. was an American mechanical engineer and management consultant who is most famous for developing the Gantt chart in the 1910s....

  • Frank Bunker Gilbreth
    Frank Bunker Gilbreth
    Frank Bunker Gilbreth, Sr. was an early advocate of scientific management and a pioneer of motion study, but is perhaps best known as the father and central figure of Cheaper by the Dozen.- Biography :...

  • Labour
  • Mechanization
    Mechanization or mechanisation is providing human operators with machinery that assists them with the muscular requirements of work or displaces muscular work. In some fields, mechanization includes the use of hand tools...

  • Productivity
    Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...

  • Scientific management
    Scientific management
    Scientific management, also called Taylorism, was a theory of management that analyzed and synthesized workflows. Its main objective was improving economic efficiency, especially labor productivity. It was one of the earliest attempts to apply science to the engineering of processes and to management...

  • Surplus value
    Surplus value
    Surplus value is a concept used famously by Karl Marx in his critique of political economy. Although Marx did not himself invent the term, he developed the concept...

  • Taylorism
  • The Mythical Man-Month
    The Mythical Man-Month
    The Mythical Man-Month: Essays on Software Engineering is a book on software engineering and project management by Fred Brooks, whose central theme is that "adding manpower to a late software project makes it later"...

    , Fred Brooks
    Fred Brooks
    Frederick Phillips Brooks, Jr. is a software engineer and computer scientist, best known for managing the development of IBM's System/360 family of computers and the OS/360 software support package, then later writing candidly about the process in his seminal book The Mythical Man-Month...

    's classic book on software engineering
  • Time and motion study
    Time and motion study
    A time and motion study is a business efficiency technique combining the Time Study work of Frederick Winslow Taylor with the Motion Study work of Frank and Lillian Gilbreth . It is a major part of scientific management...

  • Frederick Winslow Taylor
    Frederick Winslow Taylor
    Frederick Winslow Taylor was an American mechanical engineer who sought to improve industrial efficiency. He is regarded as the father of scientific management and was one of the first management consultants...

External links

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