Garment BOM: what it is and how to work it out
A garment BOM (bill of materials) is the list of every material needed to make one style: fabric, trims, labels, packing and outside processes, with the quantity used per piece. Multiply it by the order quantity and you know what to buy. Get it wrong and you either run short for one size or pay for fabric that sits in the store.
This guide explains what goes into a garment BOM, how to work out fabric consumption for woven and knit fabric, why size and colour matter, and the mistakes that cost factories the most.
What goes into a garment BOM
| Group | Examples | Usual unit |
|---|---|---|
| Fabric | Main fabric, contrast fabric, lining, rib, interlining | Metres (woven) or kilos (knit) |
| Trims | Buttons, zippers, thread, elastic, tapes, drawcords | Pieces, metres or cones |
| Labels and tags | Main label, size label, care label, hang tag, price ticket | Pieces |
| Packing | Polybags, tissue, hangers, cartons, stickers | Pieces |
| Processes | Dyeing, printing, embroidery, washing, done in-house or by a job worker | Per piece, per metre or per kilo |
Each line has a consumption (how much one piece uses), a wastage allowance and, for costing, a rate. The BOM is usually made per style, and confirmed per buyer order once sizes, colours and quantities are final.
How to work out fabric consumption
Woven fabric (metres). The most reliable way is from the marker: the cutting layout of all pattern pieces on the fabric width. If a marker for 6 shirts is 6.2 metres long, one shirt uses 6.2 ÷ 6 = 1.033 m. Add a wastage allowance for end losses, defects and cutting errors. With 5%, the BOM figure becomes 1.085 m per piece.
Knit fabric (kilos). Knits are bought by weight, so work out the area of fabric per piece (from the marker, including the waste between pieces) and multiply by the fabric weight (GSM, grams per square metre). A T-shirt that needs 1.2 m² of 180 GSM jersey uses 1.2 × 180 = 216 g. With 8% process and cutting loss, the BOM figure is about 233 g per piece.
Then scale to the order. For 1,854 pieces (1,800 ordered plus 3% excess), that is 1,854 × 1.085 = about 2,012 m of woven fabric, or 1,854 × 0.233 kg = about 432 kg of knit fabric. Subtract any free stock you already hold, and the rest is what you buy.
Why size and colour change the BOM
A single “average” per piece hides real differences:
- Fabric by size. An XL uses more fabric than an S. If the order is weighted to large sizes, an average based on M will run short.
- Trims by size. A jacket in XS may take an 18 cm zipper and in XXL a 22 cm one. Size labels are different for every size.
- Trims by colour. Thread, buttons and zippers usually match the garment colour, so each colourway needs its own lines.
That is why a garment BOM works best when each line can be tied to the sizes and colours it applies to, and its quantity follows the size and colour breakup of the order.
Allowances to include
- Cutting and end wastage on fabric (often a few percent, depending on the fabric and marker).
- Shrinkage if the fabric or garment is washed or dyed after cutting.
- Process loss when fabric goes to a dyer or printer and comes back lighter or shorter.
- Order excess for rejects and buyer allowances, usually set per size.
- Trim extras such as 2% more buttons for losses on the line: 9,270 buttons for 1,854 five-button shirts becomes 9,456.
Use your own history for these numbers. A BOM built on guessed allowances is only a guess with decimals.
From BOM to purchase
- Confirm the order quantity by size and colour, including excess.
- Approve the BOM, so purchase works from one agreed version.
- Work out the required quantity for each line, then subtract free stock that is not reserved for another order.
- Raise purchase orders from the BOM, not from memory.
- Receive by lot and inspect, so the fabric that reaches cutting is the fabric the BOM planned for.
Common BOM mistakes
- One flat average for all sizes.
- Missing small items (care labels, tapes, polybags) that stop the packing table.
- Changing the BOM after purchase without anyone seeing what changed.
- Forgetting process loss at the dyer, so the fabric comes back short.
- Copying an old style’s BOM without checking the new sizes, colours and fabric.
How Karpan ERP handles the BOM
In Karpan ERP the BOM is made per order and style. Each line can apply to chosen sizes and colours, with its own average consumption, and the BOM goes through approval. You can copy a BOM (and its planning) from an earlier order, plan the process route on a visual canvas with budget against planned cost, and raise purchase orders straight from the BOM. A purchase line cannot be reduced below what has already been received. See the BOM and planning canvas.
Questions people ask
What is BOM in garment manufacturing?
It is the bill of materials for a style: every fabric, trim, label, packing item and process needed to make one piece, with the quantity per piece and allowances for wastage.
What is the difference between a BOM and a costing sheet?
The BOM lists materials and quantities. The costing sheet adds rates, process costs and overheads to arrive at a price per piece. Many systems keep both on the same BOM by adding a rate to each line.
Who prepares the garment BOM?
Usually the merchandiser or the planning team, with fabric consumption from the pattern or CAD team and allowances agreed with production.
How is fabric consumption calculated for knitwear?
Work out the fabric area per piece from the marker, multiply by the fabric weight in GSM to get grams per piece, then add process and cutting loss.