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8s vs 12s - Some basic math

On an 8-hr schedule that is designed to cover the 168 hours of the week, one would typically need 4 people per position - or 4 crews for the entire operation. Each person/crew works an average of 42 hours a week (168 hours / 4 people). This average is achieved by working 40 hours a week 3/4 of the time and 48 hours per week 1/4 of the time.
The top schedule in the graph below shows a typical 8-hr schedule. On any given weekday 3 out of 4 people/crews are scheduled to work. Each person/crew has 7 days off per 28-day cycle.
During the entire year, each crew is scheduled to work 273 days/shifts for a total of 2184 hours. Each crew is schedule to be off work for 91 days per year.

On a 12-hr schedule that is designed to cover the same 168 hours of the week, one also typically needs 4 people/crews. Each person/crew is still scheduled to work an average of 42 hours per week (168 hours / 4 people). On a 12-hr schedule this is achieved by working 36 hours a week 1/2 of the time, and 48 hours per week the other 1/2 of the time.
The bottom schedule in the graph below shows an example for a 12-hr schedule. On any given weekday 2 out of 4 people/crews are scheduled to work. Each person/crew has 14 days off per 28-day cycle.
During the entire year, each crew is scheduled to work 182 days/shifts for a total of 2184 hours. Each crew is scheduled to be off work for 182 days per year.
For both schedules in the chart below, Sunday 7 AM was used as start of the pay week.

Posted by Rainer Guttkuhn on Tue, 9 Jun 2009