What it means
A workshop pays for machines and supervisors capable of 10,000 production hours each quarter, but customer orders use only 7,000 hours. If every cost is pushed onto the work produced, unit costs may look high while 3,000 hours of unused capacity disappear from view, and capacity cost attribution makes that split visible.
Harvard Business School discusses activity-based costing and capacity, including the value of separating unused capacity, and US Census research explores capacity costs in businesses, but a management allocation is not necessarily the required external inventory valuation. Start by defining practical capacity, because staff schedules, maintenance and normal interruptions affect how much output the resource can realistically deliver, and a theoretical 24-hour machine schedule can understate the rate if normal shutdowns make it impossible.
Then measure actual use, with production hours, machine cycles or service minutes tied to operational records for the same resource and period, and scope the resource cost pool, including salaries, depreciation, rent and other costs, to the capacity being measured. Set a capacity cost rate by dividing the chosen pool by practical capacity units, and compare it with a rate based on actual use to see the effect of idle time.
Apply the rate to resource time used and show the residual as unused capacity cost rather than silently loading it all onto products. Used-capacity cost plus unused-capacity cost should equal the relevant resource pool under the chosen method, and labour hours and machine hours are not interchangeable, so a multi-resource process may need several pools.
Check committed versus flexible cost, since a permanent lease cannot be reduced when a few hours go unused while temporary staffing may be adjusted sooner. The assigned cost of unused capacity is not automatically cash that can be saved next month, so check contracts and staffing options.
Idle capacity on one machine does not help if another process is the constraint, and idle specialist time in a service firm cannot always be reassigned, so capacity is not always fungible. Test the causes of idle time, because equipment may appear idle through defects, repair, weak sales, scheduling gaps, missing materials or customer cancellations, and planned maintenance, unplanned stoppage and lack of demand should be classified separately.
Watch short periods, since a quiet week can be normal in a seasonal business, and a recent expansion may temporarily increase unused time while demand grows. A high-volume product should not be charged for another department's idle resources merely because it is the only item sold.
Capacity attribution also helps with pricing and variances. Taking a low-price order may contribute cash while using otherwise idle capacity, but future fixed commitments and displacement risk matter, and standard costing can report under-absorbed overhead when actual activity is lower than plan, a pattern capacity attribution partly explains.
For an owner, it explains how much resource cost supported work and how much capacity was unused or reserved, and its purpose is better decisions, not a blanket instruction to cut staff.
In practice
Real-world examples.
Example
A line has 10,000 practical hours and uses 7,000, so 30% of its measured capacity is unused.
Example
A service team keeps planned reserve hours for emergency requests rather than calling them pure waste.
Example
A factory separates under-absorbed fixed overhead caused by low activity from a real utility-price increase.
Formula
Calculation
Capacity rate = Resource pool cost / Practical capacity units
Worked example. A fictional workshop has a resource pool of $200,000 per quarter and practical capacity of 10,000 hours.
- Capacity rate = $200,000 / 10,000 = $20 per hour.
- Cost of used capacity = 7,000 hours x $20 = $140,000.
- Cost of unused capacity = 3,000 hours x $20 = $60,000.
- Check: $140,000 + $60,000 = $200,000, the full pool.
- If the workshop instead divided the pool by only the 7,000 hours used, each hour would appear to cost $200,000 / 7,000 = $28.57, hiding the idle cost inside the product rate.Case study
Seen in the real world.
This entirely fictional example follows Linden Workshops. Its new production line ran below plan after a customer delayed orders. Finance used practical capacity to distinguish $140,000 of used-resource cost and $60,000 linked to unused hours, then assessed a ramp plan. It did not present the $60,000 as immediate cash savings.
The case does not prescribe inventory costing under any accounting standard. The ramp plan showed demand recovering over two quarters as the delayed orders arrived. Management kept the permanent staff, because retraining would cost more than the idle time, and used some spare hours for planned maintenance and training. It reviewed the unused-capacity figure each quarter to see whether the gap was closing.
Watch out
Common mistakes.
- Dividing resource cost by impossible theoretical hours to make products look cheap.
- Claiming all attributed idle cost can be eliminated immediately.
- Charging one active product with unrelated idle-capacity cost without disclosure.
Questions
People also ask.
Is unused capacity always waste?
No. Some may be a planned service buffer or necessary maintenance allowance.
Does the model show cash savings?
Not by itself. Test which resources can actually be reduced and when.
What capacity base should be used?
A documented practical measure suited to the resource and normal operating constraints.
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