Ask a small manufacturer what a unit costs to make and the answer is usually the materials list plus a guess. The guess is where the business lives or dies: labour, machine time, rent, power and supervision are half or more of the true cost of most manufactured products, and a manufacturer who prices from materials-plus-instinct is running a factory on a number that is wrong by design. The bookkeeping that fixes this is not exotic, three ideas carry the whole subject: a bill of materials that is actually maintained, work in progress that stops profit lying month to month, and overhead absorption that puts the factory’s real costs into the units that consumed them. This guide works through all three in plain English, with one product costed end to end.
Published: July 2026
A bill of materials is the priced recipe for one unit: every component, its quantity including expected wastage, and its current cost, at landed cost where components are imported, supplier price plus freight, duty and charges, not the invoice line alone. The BOM is the foundation of everything downstream, and it fails in two predictable ways.
A product with materials of $90 at last year’s BOM, now $108 after freight and resin increases, still quoted on the old number across 4,000 units a year, donates $72,000 of materials margin before labour and overhead are even considered. Quarterly BOM reviews on the top 20 per cent of SKUs by volume usually catch this within one buying cycle.
At any month end, a factory holds three kinds of inventory: raw materials not yet issued, work in progress, units started but unfinished, carrying their materials and the labour and overhead applied so far, and finished goods awaiting sale. Books that expense everything as spent and recognise nothing until sale produce the classic small-manufacturer pathology: a heavy production month looks like a disaster, the following sales month looks like a triumph, and neither number describes what the business actually did.
The fix is the standard flow: purchases go to raw materials on the balance sheet; materials issued to jobs move to WIP along with the labour and absorbed overhead applied; completed units move at their accumulated cost to finished goods; and cost hits the P&L as cost of goods sold only when units sell. Month end then requires an honest count or system position for all three buckets, with WIP valued at materials issued plus labour and overhead applied to date.
A job shop spends $180,000 on materials and $95,000 on production labour in March building stock for April despatches. Expensed as incurred, March shows a large loss. April ships $420,000 at strong margins and looks brilliant. With WIP, March capitalises unfinished work and April’s COGS reflects what actually shipped. Owners steering on the first version fire the wrong people and cut the wrong prices. For a small manufacturer the machinery can be proportionate: a perpetual system with job costing where volumes justify it, or a disciplined periodic method, month-end counts of raw, WIP and finished stock, priced consistently, with the movement driving COGS. What is not proportionate at any size is skipping WIP entirely.
Direct materials and direct labour are visible per unit. The factory around them, rent on the production floor, power, machine depreciation and maintenance, supervision, consumables, quality and cleaning, is just as real and belongs in the unit cost, and absorption is simply the method for putting it there.
Three steps. Pool the overheads: total the production overheads for a normal year, deliberately excluding selling and admin costs, which are period expenses, not product costs. Choose a driver: the activity that best explains how products consume the factory, direct labour hours for labour-paced plants, machine hours where machines set the rhythm. Set the rate: overhead pool divided by the normal annual quantity of the driver, then applied to every job by its hours.
The word normal is doing load-bearing work. Set the rate on normal capacity, not on a slow year’s low volumes, or the rate inflates, quotes rise, work is lost, volumes fall further, and the business prices itself into a spiral. Under-recovery in a slow year is reported as an under-absorbed overhead variance, a visible line that says the factory ran below capacity, which is management information, not a reason to reprice the catalogue.
A furniture maker produces a workshop bench. Direct materials from the maintained BOM, timber, hardware and finish at landed cost including an 8 per cent timber yield allowance: $142 per unit. Direct labour: 3.2 hours of build and finish time at a fully loaded rate of $52 per hour, wages plus super, leave loadings and on-costs, never the bare hourly rate: $166.
Overhead: the factory’s annual production overheads, rent, power, machinery depreciation, supervision, consumables, total $312,000, and normal capacity is 13,000 direct labour hours, giving an absorption rate of $24 per labour hour. The bench absorbs 3.2 hours × $24 = $77.
Full absorbed cost: $385 per unit. Priced at $560, the bench carries a true gross margin of 31 per cent. Now the point of the whole exercise: costed the way the business used to do it, materials plus a $50-an-hour labour guess and no overhead, the “cost” was $302 and the margin looked like 46 per cent. Every decision taken off that number, the discount given to win the big order at $430, the range extension into a labour-heavy variant, was made against a margin 15 points better than reality. At $430, the business believed it was making $128 a bench; it was making $45, before a dollar of selling or admin cost. Absorption costing does not change what anything costs. It ends the era of not knowing.
Same factory, a custom bench variant with 5.5 labour hours and $160 materials. Absorbed cost: materials $160 + labour $286 + overhead $132 = $578. Quoted at $620 “because materials are similar”, true margin is about 7 per cent before selling costs. The margin-by-product report kills that SKU or forces a reprice; instinct keeps selling it as a hero product.
Two disciplines keep the system honest over time. Reconcile absorbed to actual overheads at least quarterly, and investigate the variance: persistent over-recovery means the rate is padded and quotes are uncompetitive; persistent under-recovery means the capacity assumption is optimistic or the pool has grown. And use contribution thinking at the margins: for a one-off order into truly spare capacity, the incremental cost is materials and labour, and absorption is the wrong tool for that single decision, provided everyone understands that a factory priced permanently on marginal cost never pays its rent.
The manufacturer’s compliance and reporting layer inherits everything covered elsewhere on this site, with three accents. Payroll is the largest controllable cost and carries the Manufacturing Award’s classification and shift structures, with the per-payday super machinery running across the whole floor. Use the employee cost calculator when modelling loaded labour rates for BOMs. Stock control follows the distribution playbook, cycle counts, three-bucket visibility, obsolescence provisions for superseded components, with the added seam of backflushing errors where BOMs drive automatic issues. And the monthly pack worth producing: gross margin by product line at absorbed cost, WIP and finished goods movements, the absorption variance, scrap and rework as their own visible line, and labour recovery, hours charged to jobs against hours paid, the quiet metric that explains most gaps between a busy factory and a profitable one.
Expensive path: price from materials plus instinct, no WIP, no absorption. A $3 million manufacturer can misprice $100,000 to $300,000 a year of contribution without noticing until cash tightens.
Practical path: maintained BOMs, three-bucket inventory including WIP, plant-wide absorption rate, monthly margin-by-line pack. Finance support via outsourced finance services for a small manufacturer commonly sits $2,000 to $6,000 a month. Cost the finance function with the bookkeeping estimator; the hire vs outsource calculator settles the in-house question. See cost of bookkeeping in Australia and, for strategic capacity, fractional CFO costs in Australia. Job-level visibility pairs with the project profitability calculator.
Building the costing spine and running that rhythm is a defined project plus a monthly cadence, exactly the shape of work an embedded finance team delivers for small manufacturers, and it pays for itself with the first mispriced product it catches.
What is a bill of materials in bookkeeping terms?
The priced recipe for one unit: every component with quantities including wastage allowances, costed at current landed prices. It is the foundation of product costing, and it only works if it is maintained, quarterly repricing for key products, immediate repricing when major inputs move.
What counts as work in progress and why does it matter?
Units started but not finished at month end, valued at the materials issued plus labour and overhead applied so far. Without WIP on the balance sheet, heavy production months look like losses and the following sales months look like windfalls, and monthly profit stops describing performance.
What is absorption costing in simple terms?
A method for including the factory’s indirect costs, rent, power, depreciation, supervision, in unit costs: pool the annual production overheads, divide by normal capacity in labour or machine hours to get a rate, and apply that rate to each job by the hours it consumes.
Which costs should not be absorbed into products?
Selling, marketing, distribution and general administration. They are period expenses of running the business, not costs of making units, and loading them into product costs distorts both pricing and the comparison of product margins.
What does “fully loaded” labour mean?
The true hourly cost of production labour: wages plus superannuation, leave entitlements, allowances and on-costs, not the bare pay rate. Costing jobs at the bare rate understates every labour-heavy product’s cost by 20 to 30 per cent.
What is an absorption variance?
The difference between overheads absorbed into jobs and overheads actually incurred. Under-absorption signals the factory ran below the capacity the rate assumed; over-absorption signals a padded rate. Reconcile at least quarterly and treat persistent variances as information, not noise.
Should one-off orders be priced at full absorbed cost?
Not necessarily. Into truly spare capacity, the incremental cost is materials plus direct labour, and contribution pricing can be rational for a single decision. The discipline is knowing the full absorbed cost anyway, and never letting marginal pricing become the standing price list, because a factory priced at marginal cost never covers its overheads.
How does a small manufacturer start if none of this exists?
In order: build and price the BOMs for the top products, establish month-end counts of raw materials, WIP and finished goods, compute one plant-wide absorption rate from last year’s overheads and a normal capacity estimate, and re-cost the price list against the results. That sequence alone typically finds at least one product being sold below its true cost.
How often should BOMs be updated?
Top sellers quarterly, full catalogue at least annually, and immediately when a major input price moves more than a set threshold, commonly 5 to 10 per cent.
Scale Suite is a Sydney-based provider of outsourced finance teams and fractional CFO services for Australian SMEs. We deliver weekly bookkeeping, payroll, BAS/IAS lodgement, cashflow reporting, management accounts, and strategic fractional CFO oversight, all as a fully embedded team that works inside your business.
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We review and check this guide periodically. At the time of writing (July 2026), all information was current. Scale Suite is a registered BAS Agent, not a licensed tax advisor or financial advisor. This content is general information only and does not constitute professional tax, financial, or legal advice. Some details may change over time.
Scale Suite is a Sydney-based provider of outsourced finance and HR services for Australian SMEs. We deliver bookkeeping, financial reporting, payroll processing, fractional CFO support, recruitment, employee onboarding, people and culture support, and fractional HR oversight, all as a fully embedded team that works inside your business.
Employment Hero Gold Partner, CA-qualified, and Xero Certified, we replace fragmented finance and HR processes with one responsive, senior-level function at a fraction of the cost of full-time hires. We serve growing businesses across Sydney, Melbourne, Brisbane, and Perth, with packages starting from $1,500 per month and no lock-in contracts.
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