Bills of material for a small factory, with a worked example

A bill of material lists every input in one finished item, with quantity, rate and wastage. Built right, it gives you the item's cost as well as the recipe.

A bill of material (BOM) is the list of every raw material, component and packing item that goes into one finished product, with the quantity of each. For a small factory, it is most useful when each line also carries a rate and a wastage allowance. Then the same sheet tells the floor what to issue and tells you what one unit costs. Take a cotton tote bag: 0.6 metres of fabric, two handles, thread, a label and a polybag, each priced and each with a little wastage added. Add up the lines and you have the material cost of one bag.

What does a BOM actually do in a small factory?

It does two jobs at once.

It is a recipe. The person issuing material from the godown, the supervisor planning a batch and the operator on the machine all need to know what goes into the product and how much of it. If that lives only in one person's head, production stops when that person is on leave.

It is a costing document. The same quantities, multiplied by what you pay for each input, give you the material cost per unit. Without that number, your selling price is a guess, and so is the quote you give a party who asks for a bulk rate.

Many small factories keep one of these and skip the other. The floor has a recipe with no rates, and the office has a cost sheet that nobody on the floor has seen. The two drift apart, and the price you quote stops matching what you actually spend.

What goes into each line of a BOM?

Each line should answer five questions:

Column	What it means	Why it matters
Item	The raw material, component or packing item	So the godown issues the right thing
Unit	Metre, kg, piece, litre	So quantity and rate refer to the same unit
Net quantity	What ends up in one finished unit	The recipe part
Wastage allowance	Extra lost to cutting, trimming, spillage or rejects	So you issue and cost what you really use
Rate	What you pay per unit of that item	The costing part

From these you calculate two more columns: gross quantity (net quantity plus wastage) and line cost (gross quantity × rate). The total of the line costs is your material cost per finished unit.

Use the purchase rate excluding any GST you can claim as input tax credit, because recoverable tax is not part of your cost. If you are unsure which tax on your purchases you can recover, see our guide to input tax credit rules or ask your CA.

Can you show a full BOM example?

Here is a BOM for one finished item: a plain cotton tote bag with a printed logo. All figures are illustrative. Use your own quantities, rates and wastage.

Item	Unit	Net qty	Wastage	Gross qty	Rate (₹)	Line cost (₹)
Cotton fabric	metre	0.60	8%	0.648	90.00	58.32
Cotton webbing handle	piece	2	2%	2.04	4.00	8.16
Sewing thread	metre	12	10%	13.2	0.05	0.66
Printing ink	gram	6	15%	6.9	1.20	8.28
Woven label	piece	1	3%	1.03	1.50	1.55
Polybag	piece	1	2%	1.02	0.80	0.82
Material cost per bag						77.79

How to read one line: each bag needs 0.6 metres of fabric, but cutting losses mean you go through 8% more, so gross quantity is 0.6 × 1.08 = 0.648 metres. At ₹90 a metre, that line costs ₹58.32.

Now the sheet does both jobs. For a batch of 500 bags, the godown issues 500 × 0.648 = 324 metres of fabric, 1,020 handles and so on. That is the recipe at work. The office knows the material cost of the batch is about 500 × ₹77.79 = ₹38,895 before labour, power and overheads. That is the costing at work.

Notice where the money is. Fabric is three-quarters of the material cost. A small improvement in how you lay out and cut the fabric is worth more than haggling over the label. A priced BOM shows you this straight away. A quantity-only recipe never will.

How do I work out wastage honestly?

Measure it. Pick a few recent production runs and, for each main input, compare:

the quantity issued from the godown, minus anything returned unused, against
the net quantity per unit × good finished units produced.

The difference, divided by the net requirement, is your real wastage rate for that item. Count rejected finished units here too. Material that went into a bag you could not sell is still consumed.

Keep wastage on its own column instead of quietly inflating the net quantity. When it is separate, you can see it, question it and work on reducing it. When it is buried, nobody notices it creeping up.

How does a BOM connect to purchasing and stock?

Once you know gross quantity per unit, you can turn a production plan into a purchase list. Multiply planned output by each BOM line, compare with stock on hand and on order, and you know what to buy. For items you use steadily, the same consumption figure feeds your reorder point, so fabric is ordered before the cutting table runs dry.

It also gives you a check on the godown. If you produced 500 bags, the BOM says roughly 324 metres of fabric should have gone out. If your stock records show 360 metres gone, the gap is a question worth asking: higher wastage, a recording error or material leaving without a record.

Restaurants do the same thing with a recipe card per dish. If you want to see the idea in a different trade, our post on restaurant inventory and food costing works through it with ingredients and plate cost.

What are the common BOM mistakes?

Quantities without rates. A recipe-only BOM cannot tell you whether a product makes money.
No wastage column. Your costs look lower than they are, and the godown keeps "running short" for reasons nobody can explain.
Stale rates. The rate entered at launch is still there after several price increases. Update it when your purchase price moves.
Mixed units. Fabric bought by the kg but costed per metre, with no conversion written down. State the unit on every line and record any conversion factor.
Forgetting packing. Polybags, cartons, tape and labels are small per unit and large per year.
Overwriting old versions. When a design or supplier changes, save a new version with its date. You will need the old one to explain past batch costs.
One BOM for many variants. A large and a small bag are different BOMs. If you make many sizes and colours, structure them the way a size-colour matrix does, so shared lines are not retyped.

When does a simple BOM not go far enough?

A single-level BOM like the one above works well when you buy inputs and turn them into a finished product in one stage. It gets harder when you make your own sub-assemblies, for example printing panels in one section and stitching them in another, or when one process produces a useful by-product. In those cases each sub-assembly needs its own BOM, and the finished item's BOM lists the sub-assembly as one line. The principle is the same; there are just more sheets.

It also does not replace a full cost of the product. Labour, power, machine upkeep and freight sit outside the material lines. Add them below the material total so you can see both numbers.

FAQ

What is the difference between a BOM and a recipe? A recipe tells the shop floor what goes in and in what order. A BOM covers the same inputs but adds a rate and a wastage allowance for each line, so it also gives you the material cost of one finished unit. In a small factory one well-kept document can do both jobs, and it should.

How much wastage should I allow in a BOM? Use your own figure, measured. Compare the material you issued for a few production runs against the good units that came out, line by line. That gap is your real wastage. A figure copied from a supplier or another factory will be wrong for your machines, operators and material quality.

Should labour and overheads go into the BOM? The BOM itself covers materials. Many small factories add separate lines below it for labour, power and packing so the sheet shows a full cost per unit. That is fine as long as the material total stays visible on its own, because material rates change more often and need checking first.

How often should a BOM be updated? Update the rates whenever a purchase price moves noticeably, and review quantities and wastage at least every quarter or after any change of supplier, machine or design. Keep the old version with its date instead of overwriting it, so you can explain why a past batch cost what it did.