Workforce planning · Person-day arithmetic
Convert man-hours to man-days on a stated basis
Convert total person-hours into equivalent person-days using your chosen hours-per-day definition.
By HSECalc · Published
Check that this method fits your task
Workload arithmetic only. A person-day is not automatically eight hours, a calendar day or an injury-free day.
Choose your inputs and work through the steps
- Start with aggregate person-hours, not elapsed project hours. Ten people working together for one hour contribute ten person-hours.
- Write down the project definition of one person-day. Use that same definition in both the calculation and the report.
- Divide hours by the defined day length. Keep enough precision for planning, and state any rounding separately.
Equivalent person-days = total person-hours ÷ hours per person-day. This is unit conversion, not a prescribed HSE standard.
A worked example
Illustrative values explain the tool; they are not prescribed inputs for your work.
- Choose an eight-hour person-day for this fictional project.
- 400 ÷ 8 = 50 person-days.
- With a ten-hour definition, 400 ÷ 10 = 40 person-days; the workload hours did not change.
Read the result and decide what needs checking
Fifty person-days could be distributed among several people; the number does not set a project finish date. Availability, task dependencies and shift arrangements still determine the calendar.
For a comparison between projects, convert both to the same day definition. Keep the original hours so the conversion can be reproduced.
Common questions
Does 50 person-days mean 50 calendar days?
No. Several people can complete person-days of work in parallel.
Is one person-day always eight hours?
No. State the day-length definition and keep it consistent.
Does this measure injury-free time?
No. It totals workload only; it does not establish whether injuries occurred.
References and scope notes
Use the current official guidance and the instructions for your actual equipment. HSECalc is independent; a reference is not an endorsement. Read how we use methods and sources or report a correction.