Capacity is the one claim on a supplier's profile that is pure arithmetic. It can be worked back from things you can see and ask about — machines, cycle time, hours — and the answer usually differs from the number you were given.
Buyers usually ask capacity as a trust question: "what is your monthly capacity?" The answer is a claim, and it is the easiest claim in the industry to inflate, because nothing on the invoice ever contradicts it.
The useful version of the question is different. It is not how much the factory can produce. It is how much of what it produces is already promised to someone else, and where your order lands in that queue.
Take one injection moulding machine. Every figure below is something a factory will tell you without hesitation, because none of them sounds like a capacity claim.
This is why "what is your capacity" produces a marketing number. The number is usually the theoretical maximum, and the theoretical maximum assumes perfect conditions that no factory operates under.
Between the ceiling and your order sit four things: changeovers, maintenance, other customers, and yield. None of them appear in the figure you were quoted.
Ask this instead: "If I confirm today, what is the earliest date the line starts on my order?"
It is answerable, it is specific, and it is hard to fake convincingly. Read the answer like this:
Whatever the answer, follow it with: "which customers are ahead of me, and what are they making?" A factory that can name the products and roughly how long they run is describing a real schedule. A factory that says "many orders" is not.
When capacity runs short, factories do not usually say so. They accept the order and send part of it out. The part that leaves the building is where quality control stops being theirs.
Ask directly: "Which processes are subcontracted, and will any part of my order be subcontracted?" Some answers are perfectly normal — surface finishing, plating, printing and packaging are routinely outsourced even by good factories. The answer that matters is whether they will put it in writing for your order.
If a factory will not commit in writing that no part of your order is subcontracted, treat the lead time as a range with an unknown upper end rather than a date. This is the single most common way a delivery slips by a month while every message says everything is on schedule.
None of this requires expertise. It requires knowing what an empty factory looks like.
Whether the factory will protect your order when a bigger customer arrives. Whether the quoted OEE is real — 85% is a reasonable figure for a well-run plant and optimistic for a poorly run one. Whether the machines are in the condition their count implies. And whether the material feeding them is the grade you specified, which is a lab question, not a scheduling one.
What the arithmetic does give you is a ceiling you can hold the factory to. "You have five machines and each runs about 3,800 a day, so 500,000 a month is the absolute maximum with no changeovers and no other customers. You have told me you have other customers. What is realistic?" That conversation goes somewhere different from the first one.
The reason to do this is not to catch anyone. Most factories inflate the number because buyers ask for it and no one ever checks. Showing that you can check changes what you are told next — and the next thing you are told is usually the useful thing.
No supplier is identified in this entry. The figures are illustrative arithmetic for an injection moulding process, not a quotation from any named factory.
The 32-point report includes capacity against claimed capacity, because it is the cheapest claim to verify on site and the most expensive one to get wrong.
See a sample report