persondays

Person-days are a unit of effort representing the amount of work performed by one person in a standard workday. The term is used in project management, staffing, and cost estimation to express workload independent of the number of workers involved.

Calculation and example: total effort in person-days equals total hours of work divided by the number of hours in a standard workday, typically eight. For example, a workload of 120 hours equates to 15 person-days at an eight-hour day. If a project spans multiple days with differing shift lengths, the applicable hours-per-day should be specified for accuracy.

Applications: person-days are used for planning, scheduling, budgeting, and staffing. They help determine whether a given team and time frame can complete a task. For staffing, multiply the number of person-days by the intended number of workers or divide the total required person-days by the available working days to estimate headcount and duration.

Limitations and caveats: the metric assumes a constant, full-time level of productivity, which may not hold in practice. Productivity varies by task, and interruptions, learning curves, meetings, holidays, and sickness reduce effective output. Person-days do not capture complexity, quality, or risk, and should be complemented with other measures when estimating timelines and costs.

Relation to other units: one person-day typically equals eight person-hours. Related units include person-hours and person-months (roughly 160 hours for a standard full-time month, subject to organization-specific definitions). The term man-days is a historical synonym.