A working day is not always a project day
A working day may be seven or eight hours long, but that does not make the whole day available to one project.
Meetings, team coordination, code review, production support, client communication and other work reduce the time that can be assigned to the task being planned.
For delivery planning, use project capacity rather than contracted working hours.
Use a simple formula
Required working days = estimated hours ÷ available hours per day
For example:
40 hours ÷ 6 hours per day = 6.67 days
Round the result up to seven working days. At eight hours per day the same work would take five days; at four hours per day it would take ten.
The effort has not changed. The available capacity has.
Choose a value based on real work
When someone spends most of the day on one project, seven or eight hours may be realistic.
When meetings and support work happen regularly, five or six hours may be closer to reality. With several projects running in parallel, capacity can fall to two to four hours.
There is no universal number. Use a value that reflects the specific person, team and period you are planning.
Do not subtract the same time twice
If normal meetings and routine responsibilities are already reflected in lower daily capacity, do not add them again as a buffer.
Capacity describes the normal shape of a working day. A buffer covers uncertainty and possible variation. The distinction is explained in How Much Buffer Should You Add to a Project Delivery Date?.
Hours are only the first step
Once you have the number of working days, place them in the calendar. Weekends and public holidays may move the actual finish date without changing the amount of work.
The Delivery Date Calculator handles both conversions in one step.