Why the next unit can cost a lot more
Factories often add capacity in chunks. A production line, warehouse, or shift can handle only so much before it becomes a bottleneck. Below that limit, an extra unit may require little beyond more materials and machine time. At the limit, the same unit might require overtime, another shift, rented storage, or new equipment.
Economists call the cost of producing one additional unit marginal cost. It is not necessarily the factory’s typical cost per unit: it asks what changes when output rises by one. If that extra output triggers a major capacity expense, the marginal cost can jump sharply.
Capacity arrives in steps
Imagine a plant whose existing line is running nearly continuously. A small increase in orders could be manageable if workers can extend a shift. But if demand keeps rising, the plant may need a second line. That investment is a large, lumpy expense—not a smooth increase spread evenly across every unit.
The jump depends on the constraint. A factory short on machine time may need equipment; one short on floor space may need storage or a larger building. And if the expansion adds enough capacity, marginal cost may fall again for a while: the new line can produce many units before it, too, fills up.
Why the distinction matters
A business deciding whether to accept a large order should compare the revenue from the added sales with the costs those sales actually cause. Looking only at the old average cost per unit can hide an expansion bill. On the other hand, treating the entire cost of a new line as if it belonged to one unit can make that unit look impossibly expensive; the line may serve many future units.
So the meaningful question is not simply “What does this product usually cost?” It is “What extra resources will this next level of production require?” That answer can change abruptly at the moment a factory runs out of room to grow with what it already has.
