Mining Vehicle & Underground Equipment calculator

Spare Parts Inventory Calculator

Spare parts inventory sizing decides how many days a mine's stores can keep haul trucks, loaders and drills running before the next replenishment lands. Stores managers and reliability engineers use it to balance two costs that pull in opposite directions: the carrying cost of capital tied up on the shelf and the far larger cost of a machine down for want of a part. The calculation links three inputs — daily issue rate, supplier lead time and a safety cushion — into a protected days-of-supply figure that survives audit. For underground and open-pit operations where a stockout idles a production face, getting this number right is a direct lever on availability.

What this calculator does

  • Estimate spare parts inventory for mining vehicle and underground equipment using production-ready inputs so teams can plan replenishment and safety stock using actual usage and lead time.
  • Use it when spare parts inventory in mining vehicle and underground equipment is being sized for a buffer or safety stock review.
  • It calculates cycle stock as daily issue rate times replenishment lead time, adds a safety cushion, and reports the protected days of supply the stock covers.

Formula used

  • Spare parts inventory cycle stock = spare parts inventory daily usage × spare parts inventory lead time
  • Required spare parts inventory = cycle stock + spare parts inventory safety stock

Inputs explained

  • Average daily parts issue rate from stores:
  • Supplier replenishment lead time:
  • Safety stock cushion on lead-time demand:

How to use the result

  • Use it when setting reorder quantities and min/max levels for consumable and rotable spares in a mine's central or satellite stores.
  • It models a single steady issue rate, so lumpy demand from overhauls or campaign maintenance can deplete stock ahead of the protected-days estimate.

Current U.S. benchmarks

  • U.S. light vehicles sell at a 16.9 million annual rate (BEA, Jun 2026), up 4.1% from a year earlier, the volume signal for automotive supply chains.
  • Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).
  • The U.S. has 11,691 transportation equipment establishments employing about 1,682,910 workers (Census County Business Patterns, 2023).

Common questions

  • How do you calculate spare parts inventory levels? Compute cycle stock as daily issue rate times replenishment lead time, then add safety stock. At 85 units/day with a 1.1 safety factor, this model returns 12.83 protected days of supply against 14.12 unprotected days on 1200 pieces of stock.
  • What is a good days-of-supply target for mining spares? It should exceed your supplier replenishment lead time with a margin sized to demand variability. Critical, long-lead parts warrant more cover; fast-moving local-supply items warrant less.
  • How much safety stock should a mine carry? Enough to absorb demand spikes and late deliveries over the lead time. The 1.1 multiplier here adds about 10 percent; high-variability or single-source parts often justify more.
  • What is the difference between protected and unprotected days of supply? Unprotected days (14.12) is raw inventory divided by daily usage. Protected days (12.83) applies the safety factor, giving a conservative target you can actually deliver against.
  • How do I avoid overstocking spare parts? Tie stock to actual issue rates and real lead times rather than worst-case fear. Segment spares by criticality so only machine-stopping, long-lead items carry heavy safety stock.

Last reviewed 2026-05-12.