Why some businesses cost one job at a time
Earlier in this ladder you learned that the three manufacturing costs — direct materials, direct labour, and overhead — are product costs that sit in inventory until the goods are sold, while selling and admin costs are period costs expensed at once. You also learned that you must first name a cost object before any cost number means anything. Job-order costing is what happens when you point at one specific *job* and say: add up the cost of THAT. Picture a custom furniture workshop where one customer orders a walnut dining table, another a set of oak bookshelves, a third a single rocking chair. Each order eats different wood, different hours, different machine time. Dividing one month's total cost by the number of orders would be nonsense — the orders are nothing alike.
So [[job-order-costing|job-order costing]] accumulates manufacturing costs separately for each distinct job or small batch. A *job* is one identifiable unit or batch of work: a custom table, a print run of 500 wedding invitations, a single house built by a contractor, an audit engagement for one client. It is the right system whenever output is custom, distinct, or made in small batches — construction, printing, shipbuilding, film production, and professional services like law, consulting, and accounting. Its sibling, process costing, is the topic of the next guide and handles the opposite case: identical units streaming off a line where tracking one unit would be both impossible and pointless.
The job cost sheet: a mini-ledger that travels with the order
Imagine a folder that travels with each order through the workshop. Every time someone draws wood from the storeroom, that cost is written in the folder; every time a worker logs hours on this order, that labour is written in; and a calculated slice of factory overhead is added too. When the order is done, the folder shows, in one place, exactly what that order cost. That folder — paper once, a screen in software today — is the [[job-cost-sheet|job cost sheet]]. It is the detailed record for a single job, and it has three running sections: direct materials, direct labour, and applied manufacturing overhead.
Materials are written on from a *materials requisition form* — the slip a worker signs when pulling stock. Labour is written on from a *time ticket* — the record of how many hours someone spent on this job. The third stream, overhead, cannot be traced directly the way the wood and the hours can, so it has to be *applied* by a formula. Add the three sections and you have the total cost of the job; divide by the number of units in the job and you have unit cost. Here is the worked sketch the previous chapter introduced, now built one stream at a time:
JOB COST SHEET - Job 214: 500 wedding invitations -------------------------------------------------- Direct materials (card stock, ink) ........ 180 Direct labour (4 hrs x 30/hr) .......... 120 Applied overhead (4 hrs x 20/hr) .......... 80 -------------------------------------------------- Total cost of Job 214 ..................... 380 Unit cost = 380 / 500 invitations = 0.76 each
Applying overhead: the part you cannot trace
Materials and labour practically announce which job they belong to — you can watch the wood and the worker's hours go into a specific table. Overhead is the opposite: the rent, the supervisor's pay, the saw's depreciation are shared by every job and don't point at any one of them. Worse, you usually only learn the true overhead total at year-end, yet you must cost jobs all year. The fix, which you met in the glossary, is to estimate a [[predetermined-overhead-rate|predetermined overhead rate]] before the year starts: estimated total overhead divided by the estimated total of an allocation base such as labour hours or machine hours. If a factory expects 600,000 of overhead and 40,000 machine hours, its rate is 15 per machine hour.
Then, as each job runs, overhead application simply multiplies that rate by the *actual* amount of the base the job used. A job using 30 machine hours is charged 30 times 15, or 450, of overhead. Here is the honest part you must hold onto: the overhead figure on the sheet is *applied*, not actual. It is a calculated allocation built on an estimated rate — not a measured bill. Because both the estimated overhead and the estimated activity are forecasts, applied overhead almost never equals actual overhead exactly, and the gap becomes under- or over-applied overhead that is cleaned up at period-end (the next guides return to this). The number on the job sheet is never re-touched; the reconciliation happens elsewhere.
In process or complete? Where the cost lives
A job is not just a calculation — it is also a place where money sits on the balance sheet, and that place moves as the job progresses. While the job is still being worked on, it is *in process*, and its accumulated cost is part of Work in Process inventory, an asset. The moment the last task is done and the goods are ready, the job is *complete*: its whole cost moves out of Work in Process and into Finished Goods. When the customer finally buys it, that cost moves once more — out of Finished Goods and into Cost of Goods Sold, an expense. So one job's cost makes a three-stop journey: in process, finished, sold.
This is why the collection of cost sheets for unfinished jobs is not just paperwork — it literally *is* the inventory backing the Work in Process account. The total of every open job cost sheet must equal the Work in Process balance in the general ledger; if they disagree, something was posted wrong. A job that finished this month but hasn't sold yet sits in Finished Goods carrying its full cost, which is exactly why a busy workshop can spend heavily this month yet report little expense — the cost is parked in inventory, waiting for the sale, just as the product-versus-period rule promised.
- Open a job cost sheet when the job starts; it now belongs to Work in Process.
- Post direct materials from requisition forms and direct labour from time tickets as the job progresses.
- Apply overhead by multiplying the predetermined rate by the job's actual use of the allocation base.
- When complete, total the sheet and move the cost from Work in Process to Finished Goods.
- When sold, move that cost from Finished Goods to Cost of Goods Sold.
What job-order costing buys you, and where it can mislead
The payoff is concrete and auditable. With a job cost sheet a manager can quote a price knowing the cost floor, compare estimated against actual cost, spot a job that overran its budget, and bill a client honestly for time and materials. This is where the abstract idea of 'cost' becomes a real number you can defend to a customer or a court. For a contractor or a law firm, the job sheet is not optional bookkeeping — it is the very basis of the invoice.
Be honest about the limit, though. A job's cost is only as fair as the way overhead is spread across jobs — and overhead is allocated, not traced. If the chosen allocation base doesn't really drive overhead (say you spread everything on labour hours while the real cost driver is machine setups), a poorly chosen base can quietly make one job look cheap and another look expensive, distorting which jobs seem profitable. That distortion is precisely the problem a later guide in this rung — activity-based costing — was invented to address, by using several cost drivers instead of one blunt rate. Job-order costing is powerful, but its overhead figure is an honest estimate, never a fact.