What it means
The name is a picture: however wide a bottle is, liquid leaves it only as fast as the neck allows. In a factory the neck might be a single heat treatment oven; in an accounts department, the one person who can approve payments; in a hospital, the number of operating theatres; in a software team, code review.
Every process has one, because stages are never perfectly balanced. The question is whether management knows where it is.
The signs are usually visible: a queue of work in progress in front of one stage, staff at later stages waiting, overtime concentrated in one area, and a throughput rate that does not change however hard the rest of the operation works. Finding the bottleneck formally means measuring the capacity of each stage in the same units (items per hour, cases per week) and comparing it with demand.
The stage with the least spare capacity, or the largest shortfall, is the constraint. Managing a bottleneck follows a well-established sequence.
First, exploit it: make sure the constrained resource never sits idle, never processes defective work that will be scrapped, and is not used for anything a non-constrained resource could do. An hour lost at the bottleneck is an hour lost for the whole system, whereas an hour lost elsewhere costs nothing.
Second, subordinate everything else to it: schedule other stages to feed the bottleneck steadily rather than to maximise their own output, since producing more than the bottleneck can absorb only creates inventory. Third, elevate it: add capacity through overtime, a second shift, new equipment or outsourcing.
Then find the new bottleneck, because there always is one. The financial implications are large.
Because the bottleneck sets throughput, the profitability of a product should be judged by its contribution per hour of bottleneck time, not by its margin per unit. A product with a lower margin that uses little bottleneck capacity may be worth more to the business than a high-margin product that uses a lot.
Investment appraisal changes too: spending on the bottleneck pays back through the whole system, while spending elsewhere, however efficient it looks locally, may pay back nothing. Bottlenecks also move.
Relieve one and another appears, possibly in a place that was previously comfortable. A company that has doubled its machining capacity may find that its bottleneck is now inspection, then dispatch, then the sales team's ability to win orders.
The discipline is continuous.
In practice
Real-world examples.
Example
An accounts payable team processes 800 invoices a week but has a single approver who can handle 500; the bottleneck is the approval step, and hiring more data entry staff would change nothing.
Example
A software company's releases are limited by two senior reviewers; adding developers increases the queue, not the output.
Example
An airport's capacity is set by its single runway, so terminals, gates and check-in desks beyond the runway's capacity add cost without adding flights.
Think of it
“A bottleneck is the slowest point that holds everything back-your weakest link.
Formula
Calculation
System Throughput = Capacity of the bottleneck stage
Contribution per Bottleneck Hour = Contribution per unit / Bottleneck hours per unit
Worked example. A furniture workshop makes tables through four stages. Weekly capacity, in tables:
- Cutting: 120
- Assembly: 90
- Finishing (spray booth): 60
- Packing: 150
Demand is 100 tables a week. The bottleneck is finishing at 60, so the workshop can sell only 60 tables a week regardless of the other stages. If cutting and assembly run at full capacity, 30 tables a week accumulate as unfinished stock, tying up cash and space.
Exploiting the bottleneck: the spray booth is found to be idle for 8 hours a week during operator breaks and changeovers, and 5% of tables reaching it fail inspection and are re-sprayed. Staggering breaks, moving inspection before the booth and preparing the next batch during drying raise effective capacity to 72 tables a week: 12 more tables at a contribution of $180 each = $2,160 a week, or about $108,000 a year, for no capital cost.
Elevating it: a second booth costs $90,000 and would lift finishing capacity to 120, making assembly (90) the new bottleneck. Output rises from 72 to 90, an extra 18 tables a week at $180 = $3,240 a week, or $162,000 a year. Payback about seven months.
Product decision: the workshop also makes chairs at $60 contribution each, needing 20 minutes of booth time, against tables at $180 needing 90 minutes. Contribution per booth hour: chairs $60 / (20/60) = $180; tables $180 / 1.5 = $120. Per unit the table looks better; per hour of the constraint the chair is worth 50% more, so with the booth as the limit the workshop should favour chairs.Case study
Seen in the real world.
A contract laboratory was losing customers because sample turnaround had stretched from five days to twelve. Management's response had been to buy two more analysers, which made no difference. A new operations manager mapped the process and measured each stage.
The analysers had capacity for 400 samples a day against a demand of 250; the bottleneck was sample preparation, a manual step handled by three technicians with a capacity of 180 a day. Samples were queuing there for a week. She moved a technician from the analyser bench (which now had ample slack) to preparation, changed the preparation shift pattern so that the step ran ten hours a day instead of eight, and stopped preparing samples for tests that had been cancelled, which had been consuming 10% of the step's time.
Preparation capacity rose to 270 a day, above demand, and turnaround fell to four days within a month. The two extra analysers were never needed.
The cost of the improvement was a rota change; the cost of the earlier misdiagnosis was $240,000 of idle equipment. The lab now reports the capacity and queue at every stage weekly and treats the stage with the longest queue as its management priority.
Watch out
Common mistakes.
- Improving non-bottleneck stages and expecting output to rise. Local efficiency gains away from the constraint add inventory, not throughput.
- Letting the bottleneck sit idle for breaks, changeovers or rework. Every lost minute at the constraint is lost for the whole system.
- Judging products by margin per unit rather than by contribution per unit of constrained capacity.
Questions
People also ask.
How do I find the bottleneck?
Measure capacity at each stage in the same units and compare with demand; look for the longest queue and the stage where downstream staff wait.
Does removing a bottleneck solve the problem permanently?
No. Another stage becomes the constraint. Managing bottlenecks is a continuous process.
Can a bottleneck be outside operations?
Yes. Sales capacity, cash, a regulatory approval or management attention can all be the binding constraint on growth.
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