Teams & projects
Man-hours calculator
Work out the total labor in man-hours for a crew and a period, or switch mode to see how many days a job of known man-hours takes with your crew.
Total mode uses people, hours per day and days; days mode uses people, hours per day and the job's man-hours.
How man-hours are calculated
A man-hour (also called a person-hour or labor hour) is one hour of work by one person. Total man-hours are simply people × hours per person per day × days. The same unit works in reverse: if a job is estimated at a number of man-hours, divide it by the crew's combined hours per day (people × hours per day) to get the working days it takes.
Example: 5 people working 8 hours a day for 10 days put in 5 × 8 × 10 = 400 man-hours. That is 50 man-days, 10 man-weeks of five days and 2.5 man-months if a month is taken as 160 hours. Reversed, a 400 man-hour job with the same five-person crew takes 400 ÷ 40 = 10 working days, or 2 weeks; with 8 people it would take 6.25 days, and with 2 people 25.
| Unit | Equals | Note |
|---|---|---|
| 1 man-day | 8 man-hours | at an 8-hour day |
| 1 man-week | 40 man-hours | 5 days × 8 h |
| 1 man-month | 160 man-hours | 4 weeks × 40 h, common in estimates |
| 1 man-month | 173.3 man-hours | 2,080 h a year ÷ 12 |
| 1 man-year | 2,080 man-hours | 52 weeks × 40 h, before leave |
Where man-hour estimates go wrong
The arithmetic assumes the work divides perfectly between people, and real jobs rarely do. Some tasks have a fixed order (concrete must cure, code must be reviewed before release), some need one specialist, and every extra person adds coordination time. Fred Brooks described the software version in The Mythical Man-Month (1975): adding people to a late project tends to make it later, because new members need training and communication paths multiply. Use the days mode as a lower bound on duration, not a promise, and check that the crew can actually work on the job at the same time.
When you quote or invoice in man-hours, agree on the length of the working day and whether travel, setup, breaks and supervision are included; a crew on site for 9 hours with a 1-hour unpaid lunch produces 8 man-hours each, not 9. For cost, multiply man-hours by the loaded hourly labor rate, which includes employer taxes and benefits as well as wages. Tracking actual man-hours against the estimate on each job is the most reliable way to improve the next estimate.
Frequently asked questions
How do you calculate man-hours?
Multiply the number of workers by the hours each works per day and by the number of days. Four people working 7.5 hours for 6 days is 4 × 7.5 × 6 = 180 man-hours.
How many man-hours are in a man-month?
It depends on the convention. Many estimates use 160 hours (4 weeks of 40 hours); others use 173.3 hours, which is 2,080 annual hours divided by 12.
Does doubling the crew halve the time?
Only if the work can be split cleanly and people do not get in each other's way. Sequential steps, shared equipment and coordination usually mean a larger crew saves less time than the simple division suggests.