The effective number of personnel is the count used to determine certification audit time. It means all people — permanent, temporary and part-time — involved within the scope of certification, including those working on each shift.
Why it is not headcount
Two organisations with 300 employees can have completely different audit costs. If one certifies its whole operation and the other certifies a single 40-person division, the second is priced against 40 people, not 300.
Conversely, part-time and shift workers are included. A 25-person day shift running a second shift of 20 is a 45-person organisation for this purpose, not a 25-person one.
How it converts to days
IAF MD 5 sets a table of audit days against personnel bands for initial certification. As an indication: 16–25 people gives 3 days, 26–45 gives 4, 46–65 gives 5. Certification bodies then adjust within defined limits — reductions of up to 30% for factors like no design responsibility and system maturity, increases for multi-site operations, high regulation or unusually complex processes.
The practical consequence
Any consultant or certification body quoting you a precise audit fee before scope is defined is quoting an assumed personnel count multiplied by an assumed day rate. The honest sequence is scope first, then personnel, then days, then fee.