What is a bill of materials in apparel? A practical guide.

What a BOM actually is

A bill of materials (BOM) in apparel is the complete list of every component that goes into a garment - the shell fabric, the lining, the interlining, the thread, the trims, the labels, the hangtags, the polybag, the carton. With, for each of those components, how much is used, where it’s placed, who supplies it, and what it costs.

In manufacturing generally, a BOM is the recipe for a product. Apparel BOMs work the same way with one important complication: apparel is a matrix. A single style typically comes in multiple colourways and multiple sizes, so a garment BOM has to handle components that vary by colour (shell fabric, thread, contrast trim) and components that vary by size (consumption of shell fabric increases as sizes get larger). This makes apparel BOMs structurally more complex than a single-SKU BOM in most other industries.

Practically, the BOM is what turns a construction sketch into a costable, manufacturable product. Without a BOM, you can’t quote a supplier, budget a range, cost a colourway, or reconcile landed cost against target. Everything commercial about the garment is downstream of the BOM.

What goes in an apparel BOM

A complete apparel BOM has eight categories of component. Missing any of them causes a specific type of surprise later.

A useful discipline: build the BOM from the sample in front of you, not from the sketch. The sketch shows the intent; the sample shows the reality. Costing from the sketch under-counts components; costing from a fit sample includes what actually got added during development.

Consumption, wastage and yield

Consumption is how much of each component goes into one garment. For fabrics, this is metres or yards per garment - and it varies by size. For trims, it’s pieces per garment. For thread, it’s metres per seam metre.

Two important refinements:

• Wastage is what’s cut and discarded during production. For fabric, this depends on the marker efficiency, the shape of the pattern pieces and how many sizes are cut in the same lay. Typical fabric wastage is 5-15%. A BOM that assumes zero wastage under-costs materials by that much.
• Yield is how many garments actually come out of a given quantity of raw material. Yield is inversely related to wastage - 90% yield means 10% wastage - but it’s the more common term in supplier conversations.

A common BOM shortcut is to use base-size consumption for all sizes, which under-costs the extended sizes and over-costs the smaller ones. At scale this becomes a real margin distortion. A properly built BOM captures consumption per size or at minimum per size-range grouping.

Suppliers usually quote yield rather than wastage, and their yield assumptions matter: a supplier quoting on 88% yield but delivering 82% yield leaves the brand under-costed by ~7% on fabric, which for a garment where fabric is 50% of the cost is a ~3.5% hit to gross margin per unit. Verify yield in early samples.

Variant costing by colourway

Most apparel styles come in multiple colourways, and colourways often don’t cost the same. A dyed premium fabric might cost more than the same fabric undyed. A contrast trim might exist only on one colourway. A print might only be applied to certain colours. If all colourways share one costed BOM, you’re averaging - and the average might hide that one colourway is unprofitable.

Variant costing solves this by attaching per-colourway differences to a shared BOM structure:

• The base BOM lists all components shared across colourways
• Per-colourway attributes capture what differs - a different shell fabric code, a different thread colour, an additional contrast piece
• Per-colourway cost and margin are calculated separately

This matters when a range’s margin varies meaningfully by colourway. A brand launching six colourways of the same style might discover that four are healthy on margin and two are borderline - a signal to renegotiate the borderline colourways’ components or drop them from the range. Without variant costing, this insight is invisible until the season is over and the sell-through data comes back mixed.

The alternative - a duplicated full BOM per colourway - works but breaks maintenance. When a shared component’s price changes, updating six duplicated BOMs is a manual synchronisation problem that ends in inconsistency. Variant costing on one BOM handles this cleanly.

Who uses the BOM and why

The BOM isn’t just for sourcing. It’s a shared reference document used at different stages for different decisions:

• Sourcing quotes suppliers against the BOM. An incomplete BOM produces quotes with unstated assumptions - the cheapest quote often wins on assumptions that don’t hold in bulk.
• Technical design updates the BOM as construction evolves during sample rounds. Substitutions, additions and refinements all get captured on the BOM.
• Merchandising uses the costed BOM to check margin against target FOB before adopting a style. A style with promising design but broken margin can be redirected before development sinks in.
• Factory reads the BOM to cut and sew - what to procure, how much, what colour, whose supplier. The BOM is often accompanied by the factory’s own operation breakdown for labour.
• Finance reconciles landed cost against BOM cost after production. Variances flag supplier price movements, yield problems, or spec deviations.
• QC audits against the BOM to catch component substitutions - the factory used a slightly different button than specified, for instance. Common at bulk and a source of chargebacks.

Because six different teams read the BOM for six different reasons, ambiguity or omission on the BOM creates problems in six different places. That’s why BOM discipline is one of the highest-leverage habits in an apparel operation.

How the BOM connects to purchasing

The approved BOM drives raw material requirements. When a style is adopted for production and a quantity is committed, the BOM’s component list and per-garment consumption multiply out into a purchase list: for a style with 1.85m of shell fabric per garment, producing 2,000 units in that style means 3,700m of shell fabric (before wastage) to procure. Multiply this across every component on the BOM and every style in the production plan and you have the raw material requirements for the season.

How this connects to actual POs depends on the system architecture:

• Integrated PLM-ERP. Adopted BOM automatically drives supplier POs in the ERP. No re-keying. Related reading: PLM vs ERP for apparel brands.
• Separate PLM and ERP with integration. BOM data is exported from PLM as PO instructions, imported into ERP, POs are raised. Works when the integration is maintained.
• Separate PLM and ERP without real integration. BOM data is manually re-keyed as PO instructions - which introduces errors and delays proportional to how many components and how many suppliers are involved.
• No PLM, BOM in spreadsheets. Sourcing manually reads BOMs to raise POs. Doable at small scale, breaks quickly as component count and style count grow.

The BOM-to-PO handshake is one of the specific places where a well-designed apparel stack pays off, because it happens on every style, every season. Getting it wrong doesn’t manifest as one dramatic failure - it manifests as chronic small errors that add up to real cost.

Common BOM mistakes

Five patterns come up across most brands:

1. Missing components. Thread, interlining, hangtag string and packaging are the classic omissions. Nothing dramatic on any single line, but adding up to 3-8% of true garment cost that’s invisible until invoicing.
2. Consumption estimated rather than measured. Fabric consumption based on a designer’s guess rather than an actual pattern layout. Off by 15-25% is common; 40% is not unheard of on complex garments. The correction always favours “we need more fabric.”
3. No variant costing. One averaged BOM for a six-colourway style, hiding that two of the colourways are unprofitable. Fixed only by structural change to how the BOM is modelled - most spreadsheet BOMs simply can’t do variant costing well.
4. No yield or wastage. BOM cost calculated on 100% yield, which never actually happens. Result: the target FOB is chronically optimistic and every season closes with a “we didn’t hit margin, again” conversation.
5. Stale supplier prices. BOM costs based on quotes that are 6+ months old. Component markets move; fabric prices in particular can shift 10-20% in a season. A margin calculation on stale prices is fiction.

None of these are exotic. They’re what routine BOM discipline exists to prevent and what breaks when the BOM sits in a spreadsheet that no one maintains as a shared asset.

A BOM review checklist

Questions to ask before treating a BOM as costed and ready for adoption:

• Every component category covered - shell, lining, interlining, thread, trim, labels, hangtags, packaging?
• Consumption per component - measured, not estimated? Varying by size?
• Wastage or yield included on fabric consumption?
• Per-colourway variant costing where colourways differ?
• Every supplier and quoted price current within the last 3-6 months?
• Cost totalled against target FOB - and is margin visible before adoption?
• Approved and signed off by sourcing and merchandising?
• Connected to the tech pack’s construction section - what’s built and what’s costed match?

If any answer is “we’ll finalise that later,” the BOM isn’t adopted. Adopting an incomplete BOM commits the brand to landed costs that no one has actually verified.

Frequently asked questions