GlossaryKind of term: Cost and economicsBatch size
What is batch size?
Batch size is the number of parts made in one production run; it decides how many parts share the costs that fall once per batch, such as setup.
Within one batch, each setup is prepared once. It is often the quantity ordered, but need not be: you may make extra for stock or call-offs, split an order over several runs, or start a few spare parts to cover setup, first-article inspection and scrap. In the estimate, batch size separates costs per part, such as material and machining time, from costs per batch, such as setup.
How does batch size work in practice?
Costs per batch are spread over the batch size. How much they weigh per part depends on the ratio of setup time to cycle time and on the quantity: on a one-off, setup can be the largest item; on a large batch it weighs little. Batch size can also change the route: a dedicated fixture, several parts per setup, a bar feeder or a different machine can pay off at higher quantities. Spread setup over an average batch size instead of the real quantity and small batches come out too cheap, large ones too dear.
What is batch size often confused with?
Batch size is not the quantity break: the break is the set of quantities you price. Nor is it the economic batch size, the quantity at which setup and stock-holding costs together are lowest. And a batch is not a part: the part is the design, the batch is the number of copies made in one run.
How do you see batch size in Blake?
In Blake you enter the requested quantities per part. Per-piece and per-batch costs are calculated separately, with a cost estimate per piece at each quantity. More on estimating.
Frequently asked questions
What do you do when the customer gives no quantity?
Ask before you calculate. Without a quantity, the per-batch costs have nothing to be spread over, so a price per part says little. A break of two or three quantities is a common alternative.
Why is a repeat order often cheaper per part?
Because the program exists and a fixture has often been kept, so mainly setup remains, provided the first order carried those one-off costs. If the revision, machine or tooling changes, part of the programming work can come back.
Do you make exactly the quantity ordered?
Not necessarily. On new work or tight tolerances you often start one or two extra parts to cover setup and scrap, and sometimes make more for stock or call-offs. That belongs in the agreement with the customer and in your estimate.