One simple way to estimate staffing levels is to quantify labor demand and supply.
Possible factors that shape demand for employees are existing business volumes, possible expansion related growth, a favorable business climate or marketing campaign, or a reduction in sales volume owing to the impact of competition or a poor economic outlook. Possible factors that influence availability of workforce are present staffing levels less possible attrition owing to resignations, terminations, and retirements, and losses owing to transfers and promotions. One good way to prepare a staffing plan is by quantifying such factors to make an assessment.
Assume the case of a fleet operation company. The company operates 24 trucks around the clock. The total weekly man-hours required are 24 hours 24 trucks x 7 days = 4,032 hours. A normal truck driver works 40 hours. Dividing the total requirement of 4,032 by 40 hours per driver generates a requirement of 100.8, rounded off to 101 drivers.
The distortions, however, come when some drivers call in sick, or take vacation time off, or some drivers quit and finding a replacement takes time. Again, not all trucks would be running 100 times and some fleet would be idle at some point of time for maintenance or lack of business, wherein some drivers would remain idle and could proceed on vacations.
Assume the company policy may allow workers six weeks of sick leave and another two weeks of vacation time, totaling a possible eight weeks off. The total hours off per employee would be 8 x 40 = 320. For 101 employees this translate to 101 x 320 = 32,320 hours a year or (32,320 / 52) 621 hours a week. The total number of additional drivers required to cover this additional 621 hours is (621 / 40) 15.5. However, not all employees would avail or be provided with the maximum number of leaves, and the full complement of 15.5 additional employees would be unnecessary. The actual number of extra staff required depends on managerial judgment such as anticipated leave requests, the extent to which existing drivers can work overtime to cover for employees on leave, anticipated attrition, and other factors.