Enter the number of workers and hours per worker into the calculator to determine the man hours.
| Man Hours to Man Days | Man Days to Man Hours |
|---|---|
| 1 man-hour = 0.125 man-days | 0.25 man-days = 2 man-hours |
| 2 man-hours = 0.25 man-days | 0.5 man-days = 4 man-hours |
| 4 man-hours = 0.5 man-days | 0.75 man-days = 6 man-hours |
| 6 man-hours = 0.75 man-days | 1 man-day = 8 man-hours |
| 8 man-hours = 1 man-day | 1.5 man-days = 12 man-hours |
| 10 man-hours = 1.25 man-days | 2 man-days = 16 man-hours |
| 12 man-hours = 1.5 man-days | 3 man-days = 24 man-hours |
| 16 man-hours = 2 man-days | 4 man-days = 32 man-hours |
| 20 man-hours = 2.5 man-days | 5 man-days = 40 man-hours |
| 24 man-hours = 3 man-days | 6 man-days = 48 man-hours |
| 32 man-hours = 4 man-days | 7 man-days = 56 man-hours |
| 40 man-hours = 5 man-days | 8 man-days = 64 man-hours |
| 48 man-hours = 6 man-days | 10 man-days = 80 man-hours |
| 56 man-hours = 7 man-days | 12 man-days = 96 man-hours |
| 60 man-hours = 7.5 man-days | 15 man-days = 120 man-hours |
| 80 man-hours = 10 man-days | 20 man-days = 160 man-hours |
| 100 man-hours = 12.5 man-days | 25 man-days = 200 man-hours |
| 120 man-hours = 15 man-days | 30 man-days = 240 man-hours |
| 160 man-hours = 20 man-days | 40 man-days = 320 man-hours |
| 200 man-hours = 25 man-days | 50 man-days = 400 man-hours |
| Formulas: man-days = man-hours ÷ 8; man-hours = man-days × 8 (assumes 1 man-day = 8 hours; 1 man-week = 40 hours). | |
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Man Hours To Man Days Formula
MD = MH / 8
Variables:
- MD is the total Man Days
- MH is the total Man Hours
- 8 is the standard hours per man-day (adjust per your industry or country; see table below)
To convert man hours to man days, divide total man hours by the hours in a standard working day. The default of 8 hours reflects the international benchmark set by the ILO Hours of Work (Industry) Convention (No. 1) in 1919, the first binding international labor standard. The denominator is not always 8 and should match your project context.
What Are Man Hours and Man Days?
A man-hour is one unit of labor: one person working for one uninterrupted hour at average productivity. A man-day is the corresponding daily unit, typically 8 man-hours. The terms are used interchangeably with the gender-neutral alternatives person-hour and person-day in modern project documentation.
The 8-hour workday did not emerge arbitrarily. Welsh social reformer Robert Owen proposed the "8-8-8" division in 1817 (8 hours labour, 8 hours recreation, 8 hours rest). The ILO formalized 8 hours per day and 48 hours per week as the international labor standard in 1919. Ford Motor Company was among the first large industrial employers to adopt the 8-hour day commercially, in 1914, and found that output per worker increased rather than fell. The US Fair Labor Standards Act (1938) set 40 hours per week as the overtime threshold, effectively standardizing the 5-day, 8-hour workweek in American industry.
Because the man-day definition varies by country and industry, the correct denominator depends on context. The table below shows widely used standards:
| Context | Hours per Man-Day | Basis |
|---|---|---|
| US / Canada (most industries) | 8.0 h | FLSA 1938; 40-hour week standard |
| UK | 7.5 h | Working Time Regulations 1998; 37.5-hour week norm |
| France | 7.0 h | 35-hour statutory workweek (Loi Aubry II, 2000) |
| Germany | 8.0 h | Arbeitszeitgesetz; legal max 10 h/day |
| Australia | 7.6 h | Fair Work Act; 38-hour standard week |
| Japan | 8.0 h (legal) | Labour Standards Act Art. 32; actual average closer to 9-10 h |
| Offshore oil and gas (global) | 12.0 h | Shift rotation model (12 on / 12 off); 84 h/week on rotation |
| UAE construction (June to Sept) | 6.0 h outdoors | Ministry of HR midday work ban (10:00-15:00) for outdoor labor |
| OSHA safety reporting baseline | 8.0 h equivalent | 200,000 man-hour standard = 100 workers x 40 h x 50 weeks |
Man-Hours in Safety Incident Reporting
Beyond project scheduling, man-hours serve as the exposure denominator in occupational safety metrics. OSHA's Total Recordable Incident Rate (TRIR) uses the formula: TRIR = (Recordable incidents x 200,000) / Total man-hours worked.
The 200,000 baseline represents the annual man-hours of 100 full-time employees working 40 hours per week for 50 weeks (100 x 40 x 50 = 200,000 man-hours). In man-day terms, 200,000 man-hours equals 25,000 man-days, corresponding to 100 person-years of labor at a standard 8-hour day. This normalization allows companies of very different sizes to compare safety performance on a consistent basis.
Large construction and oil and gas contractors track cumulative man-hours specifically for safety milestone reporting. A widely cited benchmark is reaching 1,000,000 man-hours (125,000 man-days) without a lost-time injury. A project employing 500 workers for 250 working days at 8 hours per day accumulates exactly 1,000,000 man-hours. Contractors often publish these milestones in project communications and press releases as a measure of safety program performance.
Productive Hours vs. Contract Hours in Project Estimation
Project estimators distinguish between contract hours (the hours a worker is paid for) and productive hours (the hours generating measurable work output). Industrial projects apply a Personal, Fatigue, and Delay (PF&D) allowance, typically 10 to 20 percent, to account for tool retrieval, setup, breaks, and minor delays. A nominal 8-hour man-day therefore yields approximately 6.4 to 7.2 effective productive hours. For budget purposes, contract hours are assigned to activities; for duration purposes, calculations are based on productive hours.
In construction estimating, man-hour productivity is expressed as a unit rate: the man-hours required to install one unit of work. Representative benchmarks for process plant construction include 0.25 to 0.40 man-hours per linear foot of piping, 0.9 to 1.4 man-hours per cubic yard of structural concrete, and 12 to 20 man-hours per ton of structural steel erected. A project with 5,000 budgeted man-hours of concrete work translates to 625 man-days at 8 hours per day, or approximately 78 calendar days for a crew of 8 workers.
How to Calculate Man Hours To Man Days
- Confirm your standard man-day duration. Use 8 hours for US, Canadian, German, and Japanese projects. Use 7.5 for UK projects, 7.0 for French projects, and 12 for offshore oil and gas shifts. When in doubt, check the project schedule basis document or the applicable labor agreement.
- Calculate total man-hours. For a team: total man-hours = number of workers x average hours worked per worker. For a single worker over multiple days: total man-hours = hours per day x number of days.
- Divide total man-hours by your man-day duration to get man-days. For OSHA safety reporting, always use 8 hours as the man-day duration regardless of actual shift length, since OSHA normalizes all industries to a common 8-hour baseline for comparability.
Example: A construction project uses 15 workers on 10-hour shifts for 12 days.
- Total man-hours: 15 x 10 x 12 = 1,800 man-hours
- Man-days for scheduling (at actual 10-hour shift): 1,800 / 10 = 180 man-days
- Man-days for OSHA reporting (at standard 8-hour day): 1,800 / 8 = 225 man-days
The two figures serve different purposes. The 180 man-day figure reflects the actual calendar workload for resource scheduling. The 225 man-day figure is the exposure equivalent for safety rate calculations.
