How do you calculate stockpile inventory days?

Divide usable tons on hand by average daily draw to get raw days of cover, then divide by the safety factor for a protected figure. With 12,500 tons, 850 tons/day, and a 1.2 factor, raw cover is 14.7 days and protected cover is 12.3 days.

What does the safety factor do here?

It discounts raw days of cover to leave a buffer for higher-than-average draw or delayed resupply. A 1.2x factor turns 14.7 raw days into 12.3 protected days, so you reorder against the more conservative number.

What is usable tonnage versus total stockpile?

Usable tonnage excludes the dead heel beneath reclaim equipment, frozen or set material, and unrecoverable fines. Always enter reclaimable tons, not a survey of the whole pile, or your days of cover will be overstated.

What is a good number of stockpile inventory days?

It depends on resupply lead time and reliability: many bulk operations target 10-20 days of protected cover for rail-served feedstock and less for short-haul local supply. The 12.3 protected days in the example is reasonable if replenishment lead time is under about a week.

How do I increase days of cover without more stockpile?

Lower the daily draw (run leaner or substitute feed), improve reclaim to recover more usable tons from the same pile, or tighten resupply reliability so you can safely run a smaller buffer with a lower safety factor.

Days of cover vs reorder point?

Days of cover is the time the pile lasts; the reorder point is the tonnage at which you must trigger resupply so new material arrives before protected cover hits zero. Use protected days here, then convert lead time into a tonnage trigger.

Bulk Solids, Mining, Aggregates & Material Processing calculator

Stockpile Inventory Days Calculator

Stockpile inventory days tells you how long a pile of aggregate, ore, coal, or bulk feedstock will last at the current draw rate, expressed as days of cover. Plant schedulers and supply planners in mining and material processing use it to time replenishment, avoid run-outs that idle a plant, and right-size working stockpiles. It matters because a stockpile is both a buffer against supply interruptions and tied-up capital, and a safety factor lets you state cover conservatively. This calculator divides usable tonnage by daily usage and applies a safety multiplier so you get a protected, plan-ready number of days.

What this calculator does

Estimate stockpile inventory days for stockpile inventory days for bulk solids, mining, aggregates, and material processing using plant-floor material, production, quality, capacity, or cost inputs.
a plant team is reviewing stockpile inventory days for bulk solids, mining, aggregates, and material processing and needs a clear stockpile inventory days for production, quality, capacity, maintenance, purchasing, or costing decisions
It computes protected days of cover by dividing usable stockpile tonnage by daily draw and dividing again by the safety factor.

Formula used

Stockpile Inventory Days uses the entered stockpile inventory days for bulk solids, mining, aggregates, and material processing values on a consistent unit basis.

Inputs explained

Usable stockpile tonnage on hand:
Average daily draw from stockpile:
Safety stock multiplier:

How to use the result

Use it when scheduling deliveries or rail/truck cycles, setting reorder triggers, or checking that a stockpile can ride out a planned supply gap.
It assumes a steady daily draw; seasonal demand swings, weather that freezes or floods a pile, and unrecoverable fines mean real cover can differ from the calculated figure.

Common questions

How do you calculate stockpile inventory days? Divide usable tons on hand by average daily draw to get raw days of cover, then divide by the safety factor for a protected figure. With 12,500 tons, 850 tons/day, and a 1.2 factor, raw cover is 14.7 days and protected cover is 12.3 days.
What does the safety factor do here? It discounts raw days of cover to leave a buffer for higher-than-average draw or delayed resupply. A 1.2x factor turns 14.7 raw days into 12.3 protected days, so you reorder against the more conservative number.
What is usable tonnage versus total stockpile? Usable tonnage excludes the dead heel beneath reclaim equipment, frozen or set material, and unrecoverable fines. Always enter reclaimable tons, not a survey of the whole pile, or your days of cover will be overstated.
What is a good number of stockpile inventory days? It depends on resupply lead time and reliability: many bulk operations target 10-20 days of protected cover for rail-served feedstock and less for short-haul local supply. The 12.3 protected days in the example is reasonable if replenishment lead time is under about a week.
How do I increase days of cover without more stockpile? Lower the daily draw (run leaner or substitute feed), improve reclaim to recover more usable tons from the same pile, or tighten resupply reliability so you can safely run a smaller buffer with a lower safety factor.

Last reviewed 2026-05-12.