How to use the man-days calculator
Man-day estimating is where a schedule begins. Dividing total work quantity by the daily output of one worker gives the labor content of the task, and dividing that by crew size gives the duration. This calculator runs both steps and applies an efficiency factor along the way.
Daily output is simply the inverse of labor-hours per unit. If a database lists 1.0 labor-hour per unit and the shift is 8 hours, a worker produces 8 units per day, so either form can be entered depending on which is at hand. The efficiency factor covers the gap between ideal conditions and the real site.
The effective daily output result already includes the efficiency factor, which makes it the figure to compare against actual production reports. If actual output keeps landing below it, the assumption was optimistic and the next plan should be adjusted rather than the crew blamed.
The duration assumes the crew works evenly every day. Real production ramps up slowly at the start and tails off during punch out, so a float allowance is worth carrying. The labor cost shown here is direct wages only, with burden, overhead and profit added separately.
Frequently asked questions
Published productivity figures assume normal working conditions, so most planners apply 80 to 90 percent to allow for material waits, trade stacking and weather. Confined spaces, high work and heavy coordination pull the figure lower, and reliable historical records from similar jobs beat any rule of thumb.
Only on paper. Available work fronts are limited, so each additional worker tends to produce less than the last, and congestion eventually reduces total output. Treat the calculated duration as a best case and check how many work areas can genuinely be opened at once.
A man-day is one worker for one working day. Multiplying man-days by the length of the shift gives man-hours, which is the unit most US cost databases publish as labor-hours per unit of work. Both describe the same labor content in different denominations.