Understanding Bottlenecks and Constraints

When I read the ‘Theory of Constraints’ concepts, Initially I was not able to understand the term bottleneck and constraints clearly. I hope the same might have happened to you also. So, in this article, I am trying to provide you the definitions, in a simple way to understand them better. please let me know your feedback in the comments section below.

What is the bottleneck?

From the book ‘ The Goal’ by Eliyahu Goldratt, I understand that the author used the word ‘bottlenecks’ in many places (accurately, 182 places). The book was about a shop floor manufacturing unit which was trying to improve its performance within  3 months. The term got popular in manufacturing and management science by this book.

The neck of a bottle, always limiting the flow is called a bottleneck. As per physics, the flow of the bottle is directly proportional to the cross-sectional area of the outlet. The cross-sectional area of the outlet is directly proportional to the diameter. So, when we increase the diameter of the outlet, the area increases as well as the flow of the bottle.

In a manufacturing environment, there are many resources (for example machines) used for producing a product. All these machines are linked to produce the final product. These machines are generally with a capacity not equal to the demanded output. Supposing, the demand is 10 finished units per hour, and there are 3 machines doing 3 different processes, which are necessary to be routed through for the completion of the product.  Unless we get 10 units from each machine (process) per hour, we cannot meet my expected demand of 10 finished units per hour.

For example, if machine no.2 having the capacity to process only 6 units/ hour, then this machine is limiting the entire flow. That means irrespective of the other machines’ higher capacity, the plant can produce only 6 units/hour. So, the bottleneck here is machine 2.

The below definitions, from the theory of constraints, will be easier now for you to understand.

A bottleneck is any resource with a lower capacity than the current load.

If several bottlenecks are present in the same line of flow, the one with the least capacity is the constraint.

An hour lost on the bottleneck is an hour lost on the entire system; an hour gained on a non-bottleneck is a mirage.

What is the constraint?

All constraints are bottlenecks, but a bottleneck need not be a constraint

Dr. Goldratt coined the term constraint in his book ‘The Goal – it is not luck’.

The whole philosophy of the Theory of Constraints aims to provide the person or management to focus on important things that should be done first. It is applicable to all sectors, depts. and individual.

Since the term bottleneck has been more associated with manufacturing resources, It required to be modified to suit the resources where it is not visible to the eyes. The constraint is a higher version of the bottleneck, It specifies the elements in a system or subsystem which limits the output.

The view that a system consists of a series of dependent variables that must work together to achieve the goal and whose ability to do so is limited by some system constraint. – Eliyahu Goldratt

For example, in a manufacturing environment, a Bottleneck indicates a machine having a lower capacity. which limits the plant output.  But what about machines having a higher capacity but its outputs are limited by low market demand. The machine is not producing enough since the customer demand is less than the capacity. Here, the word constraint is more meaningful than the bottleneck.

‘The constraint in project environments is not bottlenecks but the critical path (or, more accurately, the critical chain). The constraint in the distribution has nothing to do with bottlenecks. It is either cash (wholesalers) or the number of clients that enter the shop (retail). The term bottleneck started to be misleading; it had to be replaced with the broader term constraint.’

To summarize the above, the term bottleneck indicates the resources which have less capacity to meet the demand or expected output The constraint indicates both less capacity (bottleneck) as well as the area (subsystem elements) which prevents the growth of the organization.


  1. https://www.tocinstitute.org/constraint-defition.htm
  2. Theory of Constraints Handbook by James F. Cox and John G.Schelier