BOM guide
How to write a bill of materials (BOM) for clothing
A bill of materials (BOM) is the itemized list of every material and component that goes into a garment, fabrics, trims, closures, thread, and labels, with placement, supplier, and consumption. It lets a factory quote accurately and source correctly.
What a clothing BOM includes
A complete BOM leaves nothing to interpretation. For each line item, capture:
- Component and placement, e.g. shell fabric, pocket bag, main label.
- Material / composition, fiber content, weight, or gauge.
- Color / colorway reference.
- Supplier or sourcing note, where known.
- Quantity or consumption per garment.
- Closures and trims, zippers, buttons, snaps, drawcords, with size and finish.
Common BOM mistakes
The usual errors are omissions: forgetting interlining, thread, or labels; leaving trim sizes unstated; or mixing observed and assumed materials. A factory can only quote what's on the BOM, anything missing becomes a costly assumption or a delayed sample.
Auto-drafting a BOM with SpecForm OS
SpecForm OS drafts a BOM from your garment reference, distinguishing observed structure (what it can see) from inferred detail (what it proposes) so you confirm rather than guess. It draws on a construction knowledge base for factory-accurate terminology, stitch types, closures, and trim specs, and keeps every row editable before export.
A worked BOM example, line by line
Take a simple pullover hoodie. A vague BOM says 'fleece, drawcord, zip'. A quotable BOM names each component, where it sits, what it is made of, and how much of it the style consumes. The factory reads a row and knows exactly what to source, with no follow-up email.
Here is the same hoodie written the way a sampling room wants to read it:
- Shell: 320gsm cotton/poly brushed-back fleece, 80/20, body and sleeves, roughly 1.6m per garment at the base size.
- Rib trim: 2x2 rib, 95/5 cotton/elastane, cuffs and hem, colour to match shell.
- Hood lining: self fabric or contrast jersey, state which, with placement noted.
- Drawcord: 8mm flat cotton cord, tipped ends, 1.2m, with two metal eyelets at centre-front hood.
- Zip: YKK #5 moulded, open-ended, matched to body length, pull style specified.
- Thread: matching Tex 40 for seams, Tex 60 for topstitch, listed as a line so it is never assumed.
- Main label, care label, and size label: composition, wash care, and placement all stated.
How consumption and placement affect your quote
Two BOM fields drive cost more than any other: consumption and placement. Consumption is how much of each material the garment uses, and it is what a factory multiplies by unit price to reach a fabric cost. If you leave it blank, the factory either guesses high to protect its margin or comes back with questions that stall the quote.
Placement matters because the same material behaves differently depending on where it sits. A contrast fabric used only for an inner pocket bag costs almost nothing; the same fabric used as a full body lining changes the whole costing. Stating placement per line stops the factory from over-ordering and stops you from being surprised by the price.
FAQ
Common questions
What is a bill of materials in fashion?
A bill of materials (BOM) is an itemized list of every material and component in a garment, fabrics, trims, closures, thread, and labels, with placement, color, supplier, and consumption. It's a core part of a tech pack that lets factories quote and source accurately.
How do I write a BOM for a garment?
List each component and its placement, then record material/composition, color, supplier, quantity or consumption, and any trim sizes. Include everything, shell, lining, interlining, thread, closures, and labels. Tools like SpecForm OS auto-draft the BOM from a garment photo for you to confirm.
What is the difference between a BOM and a tech pack?
A tech pack is the full manufacturing package for a style: flats, measurements, construction, and the bill of materials. The BOM is one part of that pack, the itemised list of every material and component. The tech pack tells the factory how to build the garment; the BOM tells it what to build the garment from.
How detailed does a BOM need to be?
Detailed enough that a factory can source and quote without asking you a single question. That means every component, its placement, its composition, colour, supplier where known, and consumption. If a row could be interpreted two ways, it is not finished. Interlining, thread, and labels are the lines people forget, and each one can hold up a sample.
Can I write a BOM without knowing my suppliers yet?
Yes. Early on you often know the material but not the mill. Fill in composition, weight, placement, and consumption first, and leave the supplier field as a note or 'to source'. A factory can still quote against a clear material spec and often suggests a supplier from its own base. In SpecForm OS the supplier field stays editable, so you add it later without rebuilding the row.
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