Key takeaways
Short answer: BOM and routing are the two foundational records that define a manufactured product, and they answer different questions. A bill of materials (BOM) lists what the product is made of — the components and quantities that go into it. A routing defines how it is made — the sequence of operations, the work centers, and the time at each step. The BOM is the materials structure; the routing is the process structure. Together they let a planning system work out what to buy and how long it takes. For the planning systems they feed, see ERP vs MRP.
A bill of materials is the structured list of all the components, sub-assemblies, and raw materials that go into making a product, with the quantity of each. It is the recipe in the sense of ingredients: it tells you what the product is made of and how much of each part you need to build one. BOMs are often multi-level, with sub-assemblies that have their own BOMs, forming a hierarchy from the finished product down to raw materials. The BOM's job is to define the material content of a product, which is exactly what a planning system needs to calculate material requirements — explode the BOM against a production quantity and you know how many of every component to buy or make. The BOM answers a single question: what does this product consist of? It is the materials structure, silent on how the parts are actually assembled.
A routing defines how a product is manufactured — the sequence of operations needed to make it, the work center or resource for each operation, and the time each takes (setup and run time). Where the BOM lists the ingredients, the routing is the method: the ordered steps that transform the materials into the finished product. A routing tells you that this part goes first to the cutting work center for so many minutes, then to the milling work center, then to assembly, and so on. Its job is to define the process content of a product, which is what a planning system needs to calculate capacity and schedule — the routing tells you how much time on which resources a given production quantity will require. The routing answers a different question from the BOM: not what is it made of, but how is it made? It is the process structure.
The clean distinction is that the BOM defines materials and the routing defines process — what the product is made of versus how it is made. They are complementary halves of a product's manufacturing definition, and you need both. The BOM alone tells you the components but nothing about how to assemble them or how long it takes; the routing alone tells you the steps but nothing about what materials they consume. Together they fully define the product for planning purposes: the BOM drives material requirements (what to buy and make), the routing drives capacity requirements and scheduling (how much time on which resources). Confusing or conflating them — or maintaining one accurately while neglecting the other — undermines planning: an accurate BOM with a wrong routing gives correct materials but unrealistic schedules, and the reverse gives realistic timing but wrong material orders.
Take a simple bracket assembly. Its BOM lists the materials: one steel plate, two brackets, four bolts, and a quantity of paint — that is what the assembly is made of, and exploding it against an order of 1,000 assemblies tells planning to procure 1,000 plates, 2,000 brackets, 4,000 bolts, and the paint. Its routing lists the process: operation 10, cut the plate at the cutting center (5 minutes); operation 20, form the brackets at the press (3 minutes); operation 30, assemble and bolt at the assembly station (4 minutes); operation 40, paint and cure. That is how the assembly is made, and applied to 1,000 units it tells planning how much time each work center needs, driving the schedule and capacity check. The BOM answered what to buy; the routing answered how long it takes and where. Both were essential — and both had to be accurate for the plan to hold.
The BOM and routing are the foundation that planning, costing, and scheduling are built on, so errors in either propagate everywhere. An inaccurate BOM means wrong material requirements — shortages of parts that were under-counted, excess of parts that were over-counted, and a wrong product cost. An inaccurate routing means wrong capacity and schedule — operations that take longer than planned, work centers overloaded or under-loaded, and delivery dates that slip. Because MRP explodes BOMs to plan materials and uses routings to plan capacity, the entire planning system is only as good as these two records. This is why maintaining accurate BOMs and routings is a core discipline of any manufacturer: they are not just engineering documents but the data backbone of material planning, capacity planning, costing, and scheduling. Garbage in either one becomes garbage throughout the plan.
Routings and OEE connect directly through the operation times that drive capacity planning. A routing's times define how much capacity a job is expected to need — but if a work center actually runs at a fraction of its assumed rate because of poor OEE, the real time the operation takes exceeds the routing, and the capacity plan built on that routing becomes optimistic, the same gap as capacity versus throughput and finite scheduling. Feeding real OEE into the effective capacity behind routing times is what keeps schedules achievable. The BOM, meanwhile, connects to the quality factor through scrap: when defects consume more material than the BOM assumes, material planning falls short. Accurate BOMs and routings, grounded in real OEE-adjusted capacity, are what make planning match the floor.
Fabrico measures the real performance that tells you whether your routing times reflect reality. A routing assumes a certain time per operation; Fabrico's live OEE and performance data reveal whether the work center actually achieves that rate or runs slower, exposing where routings are optimistic and capacity plans built on them will slip. By grounding the effective capacity behind your routings in real, OEE-adjusted performance, it helps keep scheduling and planning honest. Book a demo to see whether your routings match what the floor really does.
A bill of materials (BOM) lists the components and quantities a product is made of — what it consists of. A routing defines the sequence of operations, work centers, and times to make it — how it is made. The BOM is the materials structure; the routing is the process structure.
Because they define different halves of a product for planning. The BOM drives material requirements (what to buy and make); the routing drives capacity requirements and scheduling (how much time on which resources). One without the other leaves either the materials or the timing undefined.
A routing lists the sequence of operations to make a product, the work center or resource for each operation, and the setup and run time of each step. It defines the process — how the materials are transformed into the finished product, and how much time on which resources that takes.
Errors propagate through planning. An inaccurate BOM causes wrong material requirements and product costs; an inaccurate routing causes wrong capacity plans and slipped schedules. Because MRP relies on both, the whole planning system is only as good as these records.
Routing times drive capacity planning, but if a work center runs below its assumed rate because of poor OEE, the operation takes longer than the routing and the plan becomes optimistic. Feeding real OEE into effective capacity keeps schedules built on routings achievable.
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