A man-hour (sometimes referred to as person-hour) is the amount of work performed by the average worker in one

hour An hour (symbol: h; also abbreviated hr) is a unit of time conventionally reckoned as of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. There are 60 minutes in an hour, and 24 ho ...

. It is used for estimation of the total amount of uninterrupted labor required to perform a task. For example, researching and writing a college paper might require eighty man-hours, while preparing a family banquet from scratch might require ten man-hours. Man-hours exclude the breaks that people generally require from work, e.g. for rest, eating, and other bodily functions. They count only pure labor. 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 human necessities.

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, which can done by dividing the number of man-hours by the number of workers available. For example, if a task takes 20 man-hours to complete then a team of 2 people will complete it in 10 hours of work, while a team of 5 people will complete it in 4 hours. 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. Therefore, adding another person 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 In transport industry, this concept is superseded by passenger-mile and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 The units of measurement in transportation describes the unit of measurement used to express various transportation quantities, as used in statistics, planning, and their related applications. Transportation quantity The currently popular units ...

for better costing accuracy. In reality, other factors intervene to complicate 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. Economies of scale and

diseconomies of scale In microeconomics, diseconomies of scale are the cost disadvantages that economic actors accrue due to an increase in organizational size or in output, resulting in production of goods and services at increased per-unit costs. The concept of dise ...

further lead to a

non-linear In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...

relationship between the number of workers doing a given task and the amount of time it takes them to complete it. Some tasks cannot be done by less than a required minimum number of workers (e.g. lifting heavy loads) or they will be done with drastically better efficiency if the workforce exceeds a minimum efficient scale. In other cases an excessive number of workers might get in each other's way, reducing efficiency and the per person

productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...

of the individual worker. Another example is the adage, "Just because a woman can make a baby in nine months, it does not follow that nine women can make a baby in one month." This adage is often cited in systems development to 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 large

project A project is any undertaking, carried out individually or collaboratively and possibly involving research or design, that is carefully planned to achieve a particular goal. An alternative view sees a project managerially as a sequence of even ...

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 norms and economics. The average annual hours actually worked per person in employment as reported by OECD countries in 2007, for example, ranged from a minimum of 1,389 hours (in the Netherlands) to a maximum of 2,316 hours (in South Korea).

Productive system hours

The concept of productive system hours (PSH) has been used in forestry in Austria and by extension to other work. It includes time for breaks and can be used to calculate how long it may take to complete a task, including required recovery times from physically strenuous work, as well as legally required breaks or other human interactions. If it includes 15-minute breaks, it is written as (PSH15). A related concept is productive machine hours (PMH). More details in the paper "Influence of Terrain Conditions and Thinning Regimes on Productivity of a Track-Based Steep Slope Harvester".

References

Sources

''The Principles of Scientific Management''
F.W.Taylor, 1911, online
''Shop Management''
F.W.Taylor, 1911, online

online {{refend

External links