the man-hour as the conceptual multiplication of man by hour


The man-hour is a unit.

And rather than being a simple unit, like length or time or area, it is a combination of two different things: a multitude (man) and a magnitude (time).

It is not a rate like “men per hour” nor the “amount of work done per person per hour”.

Rather, the “man-hour” is a compound unit, used to compare the amount of “work” done by a person working constantly for an hour, against other tasks to be completed:

number of people × number of hours = man-hour

The concept of “man-hour” can make it easier to calculate the resources required for a project—and so it is used in project management to estimate the time and money required for various tasks.

Putting the Man-hour to Work

meauring the rate of 50 blocks per man-hour, against the workload of 200 blocks
Comparing a workrate of 50 blocks per man-hour, against a task requiring 200 blocks to be laid.

The man-hour is a unit used to measure an amount of work.

What sort of work?

Well, it depends on the context.

For a construction company, it could be “blocks laid” or “ditches dug” or “boilers installed”: any relevant amount of work, basically.

Example: a construction site foreman knows that 50 blocks can be laid by the average block-layer per hour.

That is, the average work rate is 50 blocks per man-hour.

The foreman has been asked to estimate the time to build a wall requiring 200 blocks.

How would he do this?


If 50 blocks take one man-hour, then we can compare this rate of work to the amount of work to be done: 200 blocks.

50 blocks / 1 man-hour : 200 blocks / ? man-hour

By counting off the 50 blocks against the 200 blocks, we find the 200 blocks are four times greater than the 50 blocks, in quantity: 200 blocks / 50 blocks = 200 ÷ 50 blocks / blocks = 4 blocks / blocks = 4

Thus, we need four times more man-hours.

Now the foreman knows that four man-hours are needed for the wall.

The foreman can either have one block player work on it for four hours: 1 man × 4 hours = 4 man-hours

Or the foreman can have four block layers work on it for one hour: 4 men × 1 hour = 4 man-hours

The end result is the same either way: 4 man-hours of work are needed to build the wall.

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