In short
Start from the actual workload: the annual volume of each activity times its unit time, divided by one employee’s effective working time (annual hours minus leave, public holidays, absences and training). Then add the tasks that cannot be measured and the activity peaks, and compare the result with current headcount.
1. List the activities and their volumes
List the department’s recurring activities (files handled, requests, inspections, acts) and their volume over twelve months, from registers and applications. An activity with no known volume is measured over four to six weeks before being extrapolated.
2. Measure unit times
For each activity, measure the average time to handle one case, by observation or by self-reported logs cross-checked with managers. Keep a realistic value rather than an ideal one: it must include the usual checks and back-and-forth.
3. Calculate effective working time
Start from annual working hours and subtract leave, public holidays, average absenteeism and training time. It is this available time, not the theoretical working time, that divides the workload to give the FTEs.
4. Adjust and decide
Add an allowance for tasks that cannot be measured (management, coordination, reception) and check coverage of seasonal peaks. The gap between required FTEs and actual headcount informs redeployment, recruitment or possible organizational gains.