Aftermarket, Field Service & Service Parts worked example

Spare Parts Stocking Level with on-hand spare parts of 1,600 parts: a worked example

What does the result look like when on-hand spare parts reaches 1,600 parts? The full calculation is worked below with real intermediate numbers. a spare parts planner needs to set or review stock levels for service parts supporting installed equipment

The inputs for this scenario

  • On-hand spare parts: 1,600 parts (raised for this scenario; the documented default is 620)
  • Average spare parts demand: 18 parts/day (unchanged)
  • Service-level safety factor: 1.4 x (unchanged)

Working through the calculation

  • Applying the documented formula (Unprotected stocking days = on-hand spare parts รท average daily demand) to the inputs above produces each figure below.
  • At this operating point the engine returns 63.49 stocking days for protected spare parts stocking level, the number this scenario is built around.
  • At this operating point the engine returns 88.89 days for unprotected stocking days.
  • At this operating point the engine returns 1,600 parts for on-hand spare parts.
  • At this operating point the engine returns 18 parts/day for average spare parts demand.

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 158% above the baseline at 63.49 stocking days.
  • A figure at this level is achievable when on-hand spare parts is genuinely sustained, not just peaked for a shift. It assumes steady average demand; for slow-moving or lumpy spare parts where one big repair consumes weeks of stock at once, an average-based days-of-cover figure can badly understate stockout risk.

Results at a glance

  • Protected spare parts stocking level: 63.49 stocking days (headline result)
  • Unprotected stocking days: 88.89 days
  • On-hand spare parts: 1,600 parts
  • Average spare parts demand: 18 parts/day

Run it with your numbers

  • Every input above is editable in the live Spare Parts Stocking Level calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.