Throughput, Bottlenecks, and Capacity: It’s All in the TPCBP

By Jon Miller Updated on April 4th, 2023

One of the most under-appreciated items in the Lean tool bag is the Table of Production Capacity by Process (TPCBP, also known as Process Capacity Table). This one-pager can define the theoretical maximum output of any process by taking into account manual time, cycle time, changeover time, etc.

Understanding the Formula for Capacity

The formula for capacity is simple, and intuitive once it is understood. Yet in a similar fashion to one-piece flow and takt time, there is something that seems counterintuitive or “backward” about it at first to most people. To review, the formula for capacity can be expressed as:

“Capacity = Net Available Time / Time per Piece”

To help you understand the formula for capacity, let’s break it down into its components:

Net Available Time is the amount of time available for production in a given shift, after accounting for any planned breaks and lunches. Meanwhile, Time per Piece refers to the total time required to produce one unit, including Manual Time, Auto Time, and Changeover Time.

It’s important to note that the numerator (top of the equation) is measured in seconds, while the denominator units are in seconds per piece. As a result, when you divide the two, the units of seconds cancel out, and you’re left with the number of pieces that can be produced in a given shift. In other words, the formula for capacity can be expressed as:

“Capacity = Net Available Time / (Man. Time + Auto. Time) + (Changeover Time / Pieces to changeover)”

While this formula may seem counterintuitive or backward at first, with practice, it can become much more intuitive and straightforward.

Importance of Logical Capacity Determination in Traditional Companies

This is a highly logical, fact-based way of determining the capacity of a process. For whatever reason, this is not the way most traditional companies do it.

Take the recent example of a transportation equipment manufacturer located in the mid-west U.S. The truck business has been booming since 2004, and demand has outstripped capacity by 20% or more. The company needs more throughput in order to satisfy customer demand.

Capacity Determination through Logical Process Analysis

Their Lean Manager, who has some TOC background, was pouring over data looking for the bottlenecks so that we could target kaizen activity in the right areas. This proved tricky as on different days there were problems with material shortages, poor quality of incoming materials, absenteeism, etc. All ripe areas for kaizen.

Where to Start?

One of the larger constraints appeared to be at the presses. This department was underproducing by 1,000 or more as compared to the best days in the assembly department (when all people and materials were available).

“Could we get more production out of the presses?” Of course! “But how much?” “Would it be enough or was it necessary to buy new equipment?”

When asked,

“How many more could you produce on a perfect day?”

They didn’t know. As far as the press shop was concerned, they were doing pretty good already. The closest this company could get to theoretical capacity was,

“On a good day, we can make up to 8,500 at our bottleneck process.”

The Importance of Capacity Calculation and Gemba Analysis for Process Improvement

We looked into the die changes, but those were “under control”. In other words, nobody had thoroughly calculated using the formula mentioned above. Too busy managing the day-to-day operations. When we went to the floor, collected the data, and the math was done, the theoretical capacity of the process was nearly double what they had thought. This opened people’s eyes and pointed to many areas for kaizen.

Go to Gemba, and get the facts.

Jon Miller

Jon has dedicated his 25+ year career to the field of kaizen, continuous improvement, and lean management. Jon spent the first eighteen years of his life in Japan, then graduated from McGill University with a bachelor’s in linguistics.