Mining Vehicle & Underground Equipment calculator
Spare Parts Inventory Calculator
Spare Parts Inventory sizes the stock a replenishment cycle requires, combining cycle stock across the lead time with a safety cushion. 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. 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 sizes the stock a replenishment cycle requires: daily usage across the lead time, then the safety cushion on top. Here that is 1,875 units of cycle stock and 2,062.5 units required in total.
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 (multiplier):
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 16.8 million annual rate (BEA, Jul 2026), down 1.3% from a year earlier, the volume signal for automotive supply chains.
- Steel mill PPI stands at 374.203 (BLS, Jul 2026), up 22.5% from a year earlier. New factory orders are up 7.4% 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? Cycle stock is 1,875 units across the 75-day lead time, and the 1.1 safety multiplier brings the required position to 2,062.5 units. Compare that against stock on hand plus anything already on order to see whether the next cycle is covered.
- 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 cycle stock and the required buffer? Cycle stock is what the 75-day lead time consumes on its own: 1,875 units. The required buffer adds the safety cushion on top, 2,062.5 units here, so a normal run of demand does not empty the shelf before replenishment lands.
- 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 2026-08-13.