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Since many flow units (e.g. customers in a shop, patients in a hospital) do not at all need the very same treatment or service, business processes have to serve different needs. Processing times thus might be quite different for each flow unit as well, even the path of flow units through the process might differ. For such processes with so-called multiple flow units, we need new tools to figure out which process step can bee seen as the bottleneck.

Finding the bottleneck in a multiple flow unit scenario takes four easy steps:

  • Step 1: Determine the capacity of each resource in the process (m / activity time or units per hour)
  • Step 2: Calculate the service demand for each of these resources considering multiple flow units
  • Step 3: Add multiple unit demand for every resource to calculate total demand for the resource
  • Step 4: Divide the total demand by the capacity of the resource to calculate the implied utilization

The highest implied utilization indicates the bottleneck process step. To differentiate between the implied utilization and the “regular” utilization, its best to keep this important difference in mind:

utilization = flow rate / capacity (always between 0% and 100%)

implied utilization = demand / capacity (can very well exceed 100%)

The same calculation can also be done by looking at the required work time:

  • Step 1: Determine the work time capacity of each resource (e.g. 2 workers x 60 min = 120 min)
  • Step 2: Calculate the demand for work time at each resource considering multiple flow units
  • Step 3: Add multiple unit demand for every resource to calculate total demand for the resource
  • Step 4: Divide the total workload by the available time to calculate the implied utilization


These lecture notes were taken during 2013 installment of the MOOC “An Introduction to Operations Management” taught by Prof. Dr. Christian Terwiesch of the Wharton Business School of the University of Pennsylvania at Coursera.org.

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