Opportunity Cost of Factory Space and Scarce Machine Hours

A free machine slot can still have a cost

A factory may own its machines and pay its rent in advance, yet still give up something valuable when it chooses a job. The cost is the benefit from the best feasible use that the decision excludes. That is opportunity cost.

The figure depends on the choice, the period and the alternatives. An hour left idle because there is no other useful work differs from an hour taken from a profitable order. A spare bay differs from one that could earn rent or replace paid warehouse space. Neither the machine's purchase price nor the department's overhead rate answers that question alone.

This guide uses fictional factory cases to work through those choices. All money is in currency units, or CU. The aim is to compare resource uses on a consistent basis, with each lost benefit counted once.

Define the decision before assigning a value

Start with the resource and the time for which it will be tied up. “Use the embroidery department” is too broad. “Reserve these compatible machine hours during next week's approved operating calendar” gives the calculation a boundary.

For floor space, state the area, dates and conditions of use. A bay available for three months may not support a tenant seeking a full year. A location needed for emergency access is not spare commercial space merely because it looks empty. Only feasible uses belong in the financial comparison.

Next, describe what would happen if the proposed use did not proceed. This is the baseline. It could be an existing production mix, a credible rental offer or genuinely idle capacity. The baseline should be the best available alternative under the same limits, not a weak plan chosen to make the proposal look attractive.

OpenStax's discussion of relevant information distinguishes costs that differ between choices from costs that remain unchanged. It also separates short-term operating choices from longer-term investment decisions. That distinction matters when a manager tries to apply one week's calculation to a permanent change.

For mutually exclusive uses, opportunity cost is the net benefit of the best rejected option. Do not add the benefits of several alternatives that could never have happened together. If alternatives can share the resource, compare feasible combinations instead.

The objective is to choose the better overall outcome. It is not to minimise opportunity cost in isolation. A valuable project may displace another valuable activity and still leave the factory better off.

Build the cash comparison on one basis

The examples use short periods and assume all relevant receipts and payments occur within them. They exclude tax, financing and working-capital timing differences. A real decision must include those effects where they change between options.

Here, “cash contribution” means receipts less the payments avoided if that output is not made. It is a decision measure, not the factory's reported profit. Regular payroll, existing rent and other costs that stay unchanged sit outside this comparison.

That treatment needs evidence. A cost labelled fixed may change if a new supervisor or leased unit is required. A cost labelled direct labour may remain payable when staff move between jobs. The label cannot replace a check of the actual payment.

Allocated overhead also needs care. Moving a share of head-office cost from one department to another does not, by itself, change total factory cash. If a proposal adds a real payment, include it. If it only changes the allocation, keep that accounting effect separate.

Past spending should remain visible in the records without being charged again to this decision. An old machine's book value is not the benefit lost by using it next week. A sale that the decision prevents, however, may be a real alternative and must be assessed on the right time basis.

These distinctions explain why an opportunity-cost worksheet should reconcile to a comparison of complete alternatives. A free-standing surcharge is easy to misuse. The whole comparison shows which receipts disappear and which payments actually stop.

Find the best use of a shared machine pool

Suppose a factory has 200 available machine hours next week across compatible heads. This is a pooled resource, not a claim that one machine can run for 200 hours in a week. The approved calendar already allows for required downtime. Labour, materials and downstream processes can support the plan.

Two products have credible but uncommitted demand. All output in the case is accepted, sold and paid for within the period. Unfilled demand is lost rather than delayed to another week. No existing delivery promise or penalty is displaced.

Product A earns CU 12 per garment and has CU 8 of avoidable cash payments, leaving CU 4. Product B earns CU 16 and has CU 10.40 of avoidable payments, leaving CU 5.60. These payments exclude regular payroll that stays unchanged.

The time factors cover machine occupation on the approved route within this simplified plan. They must not omit a setup or assume that an unvalidated faster method is available.

Although B earns more per garment, A earns more per scarce hour. OpenStax's constrained-resource guidance explains why contribution must be related to the limiting resource. Ranking only the garment margin would give the wrong priority here.

Make all 2,400 units of A first. They require 2,400 × 0.05 = 120 hours and contribute CU 9,600. The remaining 80 hours make 1,000 units of B and contribute CU 5,600.

The baseline therefore uses all 200 hours and produces CU 15,200 of cash contribution. Full demand for both products would require 280 hours, so the machine pool is genuinely constrained under these assumptions.

This is an allocation result, not a complete production schedule. The route, materials, quality release and timing still have to work. For related time-study terms, see ApparelDiary's SMV calculation guide.

Check what an hour means in the worksheet

Labour standard minutes and occupied machine time are different measures. If a worker can attend another task during an automatic cycle, the labour content does not describe how long the machine remains unavailable to the next job. Use the measure that matches the resource being constrained.

The same rule applies across heads. Pool hours only when the work can actually move between them under the approved method. Two machines with different attachments, capability or release status do not necessarily offer one interchangeable pool. A spreadsheet can add their calendars even when the production plan cannot use the total.

Trace the available hours to a dated calendar and the required hours to an approved route. Note whether setup, cleaning, first-off checks and expected repeat work are already included. An allowance deducted from available capacity and added again to required time may reduce the same capacity twice. An allowance omitted from both sides makes the plan too generous.

Finally, confirm the output basis. The central case uses accepted garments. If a time estimate measures starts but the sales figure counts accepted deliveries, the calculation needs a yield and repeat-work treatment. The same accepted quantity must connect demand, receipts, material use and resource hours. These checks make the opportunity cost about work the factory can truly deliver.

Price the work displaced by a new use

Now consider a new job C for 1,000 accepted garments. It needs 60 machine hours in total, including its setup and required first-off checks. It brings CU 18,000 of receipts and CU 13,000 of avoidable production payments. A separate one-time preparation payment of CU 600 is also required.

The job must be taken in full or rejected. Its net cash contribution before displacement is CU 18,000 − CU 13,000 − CU 600 = CU 4,400.

Keep A's 120 hours, since its contribution per hour exceeds B's. With C using 60 hours, only 20 hours remain for B. Those hours produce 250 garments and contribute CU 1,400.

Compared with the baseline, the factory loses 750 units of B. Their cash contribution is 750 × CU 5.60 = CU 4,200. That is the opportunity cost of C's machine time in this case.

Check the answer through the complete alternative. With C, the plan earns CU 9,600 from A, CU 1,400 from B and CU 4,400 from C. The total is CU 15,400, compared with CU 15,200 without C. The same CU 200 improvement appears.

Do not subtract B's CU 4,200 again from that total. The smaller B quantity already captures the loss. Nor should the worksheet subtract the full sales value of the displaced garments while also claiming all their avoided production payments elsewhere.

The CU 200 gain is narrow. It is a result under stated assumptions, not an instruction to accept the job regardless of risk. OpenStax's special-order discussion highlights capacity, extra fixed costs and customer effects. An actual commitment needs those questions resolved as well.

Allow for idle hours before charging for displacement

Change only available capacity to 300 hours. A and B together need 280, leaving 20 hours with no other beneficial use in this example. C still needs 60 hours, so only 40 hours displace B.

The displaced quantity is 40 ÷ 0.08 = 500 garments. Opportunity cost falls to CU 2,800, and the net benefit from C becomes CU 4,400 − CU 2,800 = CU 1,600.

The full comparison confirms it. Without C, all demand for A and B earns CU 20,800. With C, A earns CU 9,600, the remaining 1,500 units of B earn CU 8,400, and C earns CU 4,400. Total contribution is CU 22,400.

At 340 available hours, all three fit. If there is no other valuable use for those hours, C's displacement cost is zero and its net addition is CU 4,400. Its own production and preparation payments still exist.

These are separate capacity scenarios. They do not show that idle capacity always has zero value. The factory might have a credible service job, an equipment rental option or valuable maintenance work to consider. Include such alternatives when they are feasible; do not invent them merely to force a positive opportunity cost.

Test how much room the decision has for error

Return to the 200-hour case. C's CU 200 advantage disappears if its extra cash payments rise by CU 200 while everything else stays unchanged. A small unpriced inspection requirement could therefore matter more than the apparent size of its sales receipt.

Time has a similar effect. If C needs 64 hours, A still uses 120 and B receives only 16. B then makes 200 garments and contributes CU 1,120. Total contribution with C is CU 9,600 + CU 1,120 + CU 4,400 = CU 15,120, which is CU 80 below the baseline.

This sensitivity assumes the extra four hours do not themselves add cash payments. If they require overtime, consumables or external support, those payments would worsen the result further. The revised time must include any repeat checks, rework and return to the next product's setup.

Demand deserves the same scrutiny. The model assumes B's displaced sales are genuinely lost. If they can be served later without displacing later work or adding costs, the lost benefit may be smaller. If delay causes expediting costs or damages a buyer relationship, the effect may be larger. Both claims need a dated plan, not a hopeful comment.

The value of another hour is also conditional. In the original 200-hour plan, ten feasible extra hours could make 125 more units of B and add CU 700 before the cost of those hours. If all added payments total CU 500, the net gain is CU 200. That CU 500 must be additional to costs already deducted in B's contribution.

Frontline Systems' sensitivity-report guidance explains that a linear model's shadow price applies over a range. It is not a permanent market price for a resource. Once available demand is filled or another process becomes limiting, recalculate the value of extra machine time.

Check the labour basis before using a margin

A common error hides inside the contribution figure. Suppose a displaced batch would earn CU 800. Its materials and other payments that stop with the batch total CU 400. A cost sheet also charges CU 120 of regular wages, producing a reported contribution of CU 280.

If those wages remain payable while the staff do different work, losing the batch gives up CU 800 but avoids only CU 400. The cash benefit lost is CU 400, not CU 280. Using the smaller figure would treat the CU 120 as saved when it is not.

ACCA's relevant-cost guidance discusses this problem when skilled labour is diverted. The safe check is to compare the actual receipts and payments under both choices. Either adjust the contribution basis or restore the unchanged labour amount in the calculation; do not do both.

The earlier machine case avoids this trap by excluding unchanged payroll from both products' avoidable payments. That definition should travel with the worksheet whenever someone reuses its figures.

Compare three uses of one factory bay

Consider a separate three-month decision for a 300-square-metre bay. Three uses are feasible and mutually exclusive. The case assumes approved access, lease permissions and required operating conditions have already been checked. These are teaching assumptions, not permission to rent out any factory area.

Internal packing would avoid CU 18,000 of outside service payments over the period. It would add CU 5,000 of running payments and CU 1,200 of preparation cost. Its net benefit is CU 11,800.

A credible tenant offer would pay CU 4,500 a month. The factory would incur CU 700 a month of extra service costs, CU 900 to prepare the bay and CU 600 to restore it at the end. Net rental benefit is CU 13,500 − CU 2,100 − CU 900 − CU 600 = CU 9,900.

Using the bay for storage would avoid CU 7,800 of outside warehouse cost but require CU 1,300 of moves. Its net benefit is CU 6,500. All these amounts are measured over the same three months.

If the factory chooses packing, it gives up the better rejected option: CU 9,900 from tenant use. Packing improves the outcome by CU 11,800 − CU 9,900 = CU 1,900.

Adding CU 9,900 and CU 6,500 would overstate the opportunity cost. The same bay cannot deliver both rejected uses in this case. Likewise, CU 13,500 of gross rent would overstate the net benefit lost, because the rental arrangement has its own extra costs.

Suppose management accounts allocate CU 2,000 a month of existing building cost to the bay. If that CU 6,000 total stays unchanged under all three uses, it does not alter their ranking. Adding it only to packing would distort the comparison. A new payment caused by packing would be different and must be included.

Confirm that the alternative exists on the needed dates

An advertised rent is not the same as an available tenant. Before treating it as a foregone receipt, verify the proposed start, duration, payment basis and extra obligations. Include vacancy or collection uncertainty in the decision evidence rather than presenting a speculative figure as certain.

The same applies to warehouse savings. If the outside warehouse charge cannot be reduced during the next three months, moving stock inside may not avoid the stated payment. The analysis needs the terms that can actually change, including notice periods, minimum charges and moving costs.

Packing may also need more than an empty rectangle. Access routes, staging space, power, staffing and product protection affect whether the proposed activity can operate there. If another department loses useful space, its effect belongs in the comparison. Transferring congestion to a different room does not create free capacity.

At the end of the period, the uses must return the factory to comparable states or account for the difference. Restoration cost is explicit in the tenant case. If packing leaves equipment that blocks the next planned use, include the removal cost and any lost time as well.

Know when one-resource ranking is insufficient

The machine example has one binding production resource and fixed demand limits. Real factories may face several limits at once: machine time, skilled labour, material availability and finishing capacity. A product attractive per machine hour can be unattractive per scarce labour hour.

ACCA's linear-programming guide shows how an objective and several resource constraints can be modelled together. It also explains why quality and supply reliability remain relevant to decisions about extra resources. A numerical optimum does not remove those conditions.

Whole batches, fixed setup costs and minimum commitments can also break a simple ranking rule. C was assessed as a complete job, including its one-time cost, rather than treated as an unlimited stream of identical units. More complex combinations may require an integer model or an explicit comparison of feasible plans.

For decisions lasting years, use dated incremental cash flows and assess risk, tax and residual values. Do not carry a short-period contribution rate into a long-term investment case unchanged. ApparelDiary's capacity-investment decision trees can help structure different demand outcomes.

Keep the comparison useful after approval

Save the baseline plan alongside the selected one. Record the capacity period, demand evidence, time basis and costs assumed to change. The person reviewing the result should be able to trace the CU 4,200 displacement in the machine case to 750 lost units of B, not just to a typed surcharge.

Separate known commitments from estimates. In the bay case, a written rental offer, a warehouse cancellation term and a budgeted service charge carry different kinds of uncertainty. Give each assumption a source and a date. Recheck it when the decision date or operating period changes.

After implementation, compare actual use and cash effects with the approved case. A job that takes extra hours may lose its small expected advantage even if its own invoice margin remains positive. A bay that sits empty during a tenant delay may have a lower alternative value than first expected.

Opportunity cost makes those trade-offs visible. It is most useful when the reader can see the feasible alternative, the benefit given up and the costs that truly change. That is a stronger basis for choosing a resource use than either “we already own it” or an unexplained overhead charge.

References

• OpenStax: Identify Relevant Information for Decision-Making.

• OpenStax: Evaluate and Determine How to Make Decisions When Resources Are Constrained.

• OpenStax: Evaluate and Determine Whether to Accept or Reject a Special Order.

• ACCA: Relevant costs.

• ACCA: Linear programming.

• Frontline Systems: Excel Solver, Interpreting the Sensitivity Report.