Idle Capacity
Definition
Idle capacity is the portion of available production capacity that is not being used — machines, labor, or facilities standing ready but unassigned to work — usually expressed as available hours minus scheduled hours.
In Practice
A work center staffed and equipped for 160 hours a week but loaded with 120 hours of orders carries 40 hours of idle capacity, a 25% idle rate. Some idleness is deliberate — protective capacity held against variability, or surge capacity for peak season — while unplanned idleness signals weak demand, poor scheduling, or an unbalanced line.
Idle capacity carries real cost: depreciation, leases, and salaried labor continue whether or not output is produced, which is why accountants track the cost of idle capacity separately rather than burying it in product overhead rates. Planners distinguish idleness at the bottleneck (lost throughput forever) from idleness at non-constraints (often harmless and cheaper than building excess inventory).
Frequently Asked Questions
Is idle capacity always bad?
No. Idleness at non-bottleneck resources is often the correct outcome — running them flat out would only build work-in-process the constraint cannot absorb. Deliberate idle capacity also serves as protection against demand surges and disruptions. Idleness at the bottleneck, however, is throughput lost permanently.
How is idle capacity costed?
Good practice charges the cost of unused capacity — the fixed depreciation, lease, and staffing cost of the idle hours — to a separate variance account rather than loading it into product overhead rates. Otherwise low volume inflates unit costs, prices rise, volume falls further, and the spiral repeats.
Related Terms
Productive capacity is the portion of a resource's capacity actually used to produce saleable output — the hours generating throughput, as distinguished from idle capacity and protective capacity held in reserve.
Protective CapacityProtective capacity is extra capacity deliberately maintained at non-bottleneck resources so they can catch up after disruptions and keep the constraint continuously supplied, protecting system throughput from normal variability.
Surge CapacitySurge capacity is the ability to rapidly scale output above normal levels for a short period — through overtime, extra shifts, temporary labor, or outsourcing — to absorb demand peaks or recover from disruptions.
Idle TimeIdle time is time during which a worker or machine is available but not producing — waiting for materials, instructions, setups, repairs, or upstream work — representing paid capacity that generates no output.