Aftermarket, Field Service & Service Parts worked example

Spare Parts Stocking Level with on-hand spare parts of 310 parts: a worked example

This worked example runs the spare parts stocking level numbers for a tougher week than the baseline: on-hand spare parts of 310 parts instead of the typical 620 parts. Calculate protected stocking days for spare parts from on-hand stock, daily demand, and a service-level safety factor.

The inputs for this scenario

  • On-hand spare parts: 310 parts (the input this scenario stresses; the baseline uses 620)
  • Average spare parts demand: 18 parts/day (held at the documented default)
  • Service-level safety factor: 1.4 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Unprotected stocking days = on-hand spare parts รท average daily demand.
  • Protected spare parts stocking level works out to 12.3 stocking days at these inputs, and this is the headline figure for the scenario.
  • Unprotected stocking days works out to 17.22 days at these inputs.
  • On-hand spare parts works out to 310 parts at these inputs.
  • Average spare parts demand works out to 18 parts/day at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where on-hand spare parts sits at 620 parts and the headline result is 24.6 stocking days, this scenario comes in 50% below the baseline at 12.3 stocking days.
  • Use it when setting reorder points, sizing safety stock for critical SKUs, or auditing whether a depot is over- or under-stocked relative to service-level targets. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Protected spare parts stocking level: 12.3 stocking days (headline result)
  • Unprotected stocking days: 17.22 days
  • On-hand spare parts: 310 parts
  • Average spare parts demand: 18 parts/day

Run it with your numbers

  • To rerun this with your own numbers, open the live Spare Parts Stocking Level calculator, set on-hand spare parts to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.