Calculating Direct Material Costs in Unit Costing

Every product a company sells starts with something it bought – wood for furniture, cotton for shirts, steel for machinery parts. But how much of that buying actually ends up in what got made this month? That single number, the cost of materials consumed, decides whether your entire cost sheet is accurate or way off. Get this calculation wrong, and every cost figure built on top of it – prime cost, cost of production, even the selling price – goes wrong too.

What direct materials actually cover 🔗

Direct materials are the raw materials and components that become part of the finished product and can be traced to it without guesswork. Wood in a table, fabric in a shirt, steel in a machine part – all direct materials. Glue, lubricating oil, or factory cleaning supplies are indirect materials because you cannot trace an exact quantity to a single unit produced.

This distinction matters because only direct material cost enters prime cost. Indirect materials get bundled into factory overheads instead. So before you calculate anything, the first job is sorting materials into the right bucket.

What gets added to the material’s price 🔗

The cost of a direct material is rarely just its invoice price. According to AccountingTools, import duties, handling and storage costs directly tied to making the material usable, and insurance paid while goods are in transit all form part of direct material cost. In an Indian setting, this list usually includes customs duty on imported inputs and any non-creditable portion of GST.

On GST specifically, the treatment depends on whether input tax credit is available. Where a business can claim input tax credit on the GST paid on raw materials, that GST amount does not become part of the material cost – it sits in the credit ledger and gets set off against output GST. But where credit is blocked, as explained by Patron Accounting, the GST paid gets added to the purchase cost and becomes part of what flows into cost of materials consumed. This one rule trips up a lot of students who assume GST is always excluded.

The formula for cost of materials consumed 🔗

Once you know what counts as a direct material, the calculation itself is a straightforward stock-flow equation:

Cost of Materials Consumed = Opening Stock of Materials + Purchases + Carriage Inwards − Closing Stock of Materials

Think of it as tracking everything that was available for use during the period, then subtracting whatever is still sitting unused in the stores at the end. What’s left is what actually went into production.

Opening stock 🔗

This is the value of direct materials lying in the stores at the start of the period – essentially last period’s closing stock carried forward. It is valued at whatever method the business consistently uses, commonly First-In-First-Out or weighted average cost.

Purchases 🔗

This covers all direct materials bought during the period, net of purchase returns and trade discounts. If a business returned defective material worth ₹5,000 to a supplier, that amount reduces the purchases figure before it enters the formula. Cash discounts, on the other hand, are usually treated as a financial gain and kept out of the material cost calculation, since they reward prompt payment rather than reduce the material’s actual worth.

Carriage inwards 🔗

Carriage inwards is the freight and transport cost paid to bring materials from the supplier to the factory. Because it is incurred by the buyer to make the material available for use, it is treated as a direct cost and added to the material’s value, unlike carriage outwards – the cost of delivering finished goods to customers – which is a selling expense and never touches material cost. As Physics Wallah notes, this is precisely why the two terms are commonly tested together in exams – students often mix up which one adds to inventory and which one hits selling expenses.

Closing stock 🔗

Closing stock is the value of direct materials still lying unused at the end of the period. It has to be subtracted because those materials were available but not actually consumed in production – they will show up in next period’s opening stock instead.

Putting the formula to work 🔗

Say a furniture manufacturer starts the month with wood inventory worth ₹50,000. During the month, it purchases additional timber worth ₹1,80,000 and pays ₹8,000 as transport charges to get the wood to the factory. At month-end, ₹30,000 worth of wood remains unused in the stores.

That ₹2,08,000 is the real material cost for the month – not the ₹1,80,000 that was purchased, and not the ₹50,000 the business started with. Mixing up “purchases” with “materials consumed” is one of the most common errors students make in unit costing problems, and it throws off every cost figure that follows.

Why this number decides your prime cost 🔗

The Institute of Chartered Accountants of India defines prime cost as the sum of direct material cost, direct employee cost, and direct expenses. Cost of materials consumed is the direct material figure that feeds directly into this line. If that figure is wrong, prime cost is wrong, and since factory overheads in a cost sheet are frequently absorbed as a percentage of prime cost, that single error cascades through cost of production, cost of goods sold, and finally the selling price you quote a customer.

This is also why cost accountants take material reconciliation seriously. A discrepancy between the physical stock count and the book figure for closing stock – due to pilferage, evaporation, or breakage – needs to be identified and adjusted separately as abnormal loss, rather than silently absorbed into the consumption figure. Otherwise, normal production costs end up inflated by losses that have nothing to do with actual manufacturing.

A note on valuing the stock figures 🔗

Opening and closing stock are rarely bought at a single price – materials get purchased in batches at different rates over time. So the method used to value stock affects the final consumption figure. Under FIFO (First-In-First-Out), the oldest purchase cost is assumed to be used up first, so closing stock reflects more recent, often higher, prices. Under weighted average cost, all purchases are pooled and an average rate is applied. As per NetSuite’s guide on direct material costs, consistency in the valuation method matters more than which one is chosen, since switching methods between periods makes cost trends impossible to compare meaningfully.

Common mistakes to watch for 🔗

A few errors show up repeatedly in unit costing problems:

• Treating carriage outwards as a material cost: only carriage inwards belongs in this calculation.
• Ignoring purchase returns: returned material must reduce the purchases figure, not just disappear from inventory records.
• Using total purchases instead of consumption: a business can purchase far more than it actually uses in a period.
• Forgetting GST treatment: creditable GST should not sit inside material cost, while non-creditable GST should.

Working through a few practice problems with different combinations of returns, discounts, and carriage charges is the fastest way to make this formula second nature rather than something you have to re-derive every time.

What do you think? If a business switches its stock valuation method from FIFO to weighted average halfway through the year, how might that affect the comparability of its cost sheets across periods? And where do you think abnormal material losses, like theft or spoilage, should actually be shown in a cost sheet?

References

1. https://www.accountingtools.com/articles/what-are-direct-materials.html
2. https://www.patronaccounting.com/glossary/accounting/cost-of-goods-sold
3. https://www.pw.live/commerce/exams/difference-between-carriage-inwards-and-carriage-outwards
4. https://resources.catestseries.org/ca-inter-costing-chapter-6-cost-sheet-by-icai-1770720446.pdf
5. https://www.netsuite.com/portal/resource/articles/accounting/direct-material-costs.shtml