Man-Hours Calculator (crew size, days & job hours)

Understanding the man-hours calculator — concept and principle

This calculator works out how many man-hours (person-hours) a crew provides, how many of them are productive, and, for a job of known size, how many workers or days you need. Site managers, contractors, event organisers and project planners use it to staff jobs and check schedules.

People × hours × days — with the default inputs: 12 h to spare.

How it is calculated

Total man-hours = workers × hours per worker per day × working days
Productive man-hours = total × productive share %
Man-days = total man-hours ÷ hours per day
Workers needed = job size ÷ (hours per day × days × productive share), rounded up
Days needed = job size ÷ (workers × hours per day × productive share)
Hours left over = productive man-hours − job size (negative = short)

The principle

A man-hour is one person working for one hour, the basic unit of labour input used in labour statistics and planning. Multiplying crew size by hours and days gives the total time bought. Not every paid hour goes into the job: breaks, setup, travel and waiting take a share, which is why the productive share matters. The arithmetic assumes the work can be shared evenly among people. That is true for many tasks but not all: adding people to work that cannot be split, or that needs training and coordination, does not shorten it in proportion.

Worked example

Defaults: 6 workers, 8 hours a day, 15 days, 85% productive, job of 600 productive hours.

Total man-hours = 6 × 8 × 15 = 720; man-days = 720 ÷ 8 = 90.
Productive man-hours = 720 × 0.85 = 612.
Workers needed = 600 ÷ (8 × 15 × 0.85) = 600 ÷ 102 = 5.88, rounded up to 6.
Days needed with 6 workers = 600 ÷ (6 × 8 × 0.85) = 600 ÷ 40.8 = 14.7.
Hours left over = 612 − 600 = 12.

Each point is the calculator re-run with only “Number of workers” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Number of workers	Total man-hours
1.5	180
3	360
4.5	540
6	720
7.5	900
9	1,080
12	1,440

How to read the result

A small positive leftover, as here, means the plan works but with little slack: about one and a half crew-days. A negative figure means the crew will run short unless you add people, extend hours or days, or raise productivity. When planning critical jobs, keep a margin for sickness, weather and rework.

Common mistakes

Using 100% productive time when breaks and setup are unavoidable.
Assuming doubling the crew halves the time for every task.
Counting overtime hours without adjusting for fatigue.
Mixing productive hours in the job estimate with paid hours in the crew plan.

Keep in mind: Labour law limits working hours and requires rest. Check local rules before planning long days or weeks.

Frequently asked questions

What is a man-hour?

One person working for one hour. Many organisations now use the neutral term person-hour.

How do I convert man-hours to man-days?

Divide by the hours in a working day, here 8.

Why does adding workers not always speed up a job?

Some tasks cannot be split, and extra people need coordination and space.

Sources: U.S. Bureau of Labor Statistics, hours-worked measures (person-hours as a unit of labour input)

Checked 9 Nov 2026. Definition of the person-hour as a unit of labour input (hours worked × persons, as in national labour statistics such as the BLS hours-worked measures); planning arithmetic only.

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