The most efficient shift length (one that requires the fewest staff) depends the nature of the hourly coverage requirements, i.e. whether the coverage needs are constant or vary on a regular basis throughout the day. It doesn't matter if the group operates 24/7 or something less than that. Here's a flow chart of the steps involved:

24/7 Operations

If the coverage requirements are steady throughout the day, then the best choice is either 8-hour or 12-hour shifts. That's because these shift lengths don't overlap during the 24-hour day. Other shift lengths (9, 10, or 11 hours) would overlap. This not only doubles the coverage during the overlap(s), but it also increases the staffing requirements. Three 9-hour shifts require 12.5% more staff, three 10-hour shifts require 25% more staff, and three 11-hour shifts require 37.5% more staff.

If the coverage requirements vary fairly regularly by time of day, the organization can either use:

• Fixed shifts with different staffing levels on each shift that match the coverage requirements, e.g., 4 people on day shift, 3 people on evening shift, and 2 people on night shift.
   
• Overlapping shifts, e.g., 9 or 10-hour shifts. By changing the shift start and end times, the daily overlaps can be consolidated and matched to the busy period.
   
• An overlay shift that boosts the coverage for the length of that additional shift, e.g., a 6-hour shift from 3 p.m. to 9 p.m.

Less than 24/7 Operations

If the coverage requirements are steady, the best choice would be a shift length that matches the hours of operation - up to a maximum of 12 hours. For example, if the company is open for 11 hours a day, the most efficient choice would be an 11-hour shift, since this would require the smallest number of employees and would avoid any overlapping shifts. If the daily hours exceed 12 hours, then 2 shifts are needed each day. For example, a company that is open 14 hours a day could have two 7-hour shifts or one 8-hour shift and one 6-hour shift.

If the coverage requirements vary by time of day, the organization can either use:

• Fixed shifts with different staffing levels on each shift that match the coverage requirements, e.g., 2 people on the first shift and 4 people on the second shift.
   
• Overlapping shifts. For example, if the late afternoon is busiest, a company could use a 12-hour day shift and an 8-hour evening shift that overlaps from 4 p.m. to 8 p.m.
   
• An overlay shift that boosts the coverage for the length of that additional shift, e.g., a 4-hour shift from 3 p.m. to 7 p.m.

Summary

If you want to maximize employee utilization, your shift length should be based on the whether the workload and associated coverage requirements remain steady throughout the day or vary on a fairly regular basis. Steady workloads should have shifts that don't overlap for more than the length of a meal break. Variable workloads can be addressed in several different ways.

Many people choose the shift length for other reasons. For example, they choose 10-hour shifts, hoping to get an extra day off each week, or they choose 12-hour shifts, hoping to get more weekends off. They don't realize that this may increase the headcount requirements, not match the coverage with the workload, or utilize the staff ineffectively.