How do you calculate silo days of supply?

Divide current inventory by the daily draw-down rate. At 320 tons on hand drawing 45 tons per day that is about 7.1 days of supply; subtract a 3-day safety buffer and you have roughly 4.1 protected days.

What is a good safety stock buffer for a silo?

Set it to at least your supplier's worst-case replenishment lead time plus a margin for weather or rail delays. Three days is light for rail-served minerals; truck-served local material can run leaner.

When should I reorder bulk mineral for a silo?

Reorder when days of supply falls to your safety buffer plus lead time. If protected days hits zero, you are inside the buffer and any delivery slip risks a stockout.

Days of supply vs protected days, what is the difference?

Days of supply is the raw runway from current tonnage; protected days subtracts the safety buffer to show how much true slack you have before you eat into the floor that covers delivery lead time.

Why does a constant draw-down assumption matter?

If you add a shift or ramp throughput, daily draw-down rises and the same tonnage covers fewer days. Recalculate whenever the production rate changes, not just when inventory changes.

What does negative protected days mean?

It means your on-hand supply is already below the safety-stock floor; you are running on the buffer itself and must expedite a delivery immediately.

Industrial Minerals & Powder Processing calculator

Silo Inventory Days Calculator

Silo Inventory Days converts your current silo tonnage and daily draw-down rate into how many days of production you can run before the silo empties, then nets out a safety-stock buffer to show your true protected runway. Plant schedulers and supply planners at cement, lime, frac-sand and mineral-filler operations use it to decide when to call the next rail or truck delivery. With long-lead bulk minerals, running a silo dry stalls the whole downstream line, while overfilling risks bridging and compaction. This calculator gives the scheduler a single number to trigger reorders against supplier lead time.

What this calculator does

Calculate how many days of production or shipment a mineral storage silo can cover based on usable capacity, current inventory, and daily draw-down rate.
Use it when an operations manager or logistics planner needs to schedule silo refills, plan truck or railcar deliveries, or set safety stock levels for ground limestone, calcium carbonate, silica, or other stored mineral products.
It divides current silo inventory by the daily draw-down rate to get days of supply, then subtracts the safety-stock buffer to show days above the floor.

Formula used

Days of supply = current silo inventory / daily draw-down rate
Days above safety stock = days of supply - safety stock buffer

Inputs explained

Daily draw-down rate:
Current silo inventory:
Safety stock buffer:

How to use the result

Use it daily or per shift to decide whether to place a replenishment order against your supplier's lead time.
It assumes a constant draw-down rate; a sudden production ramp or a second shift will shorten real runway well below the calculated days.

Current U.S. benchmarks

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).

Common questions

How do you calculate silo days of supply? Divide current inventory by the daily draw-down rate. At 320 tons on hand drawing 45 tons per day that is about 7.1 days of supply; subtract a 3-day safety buffer and you have roughly 4.1 protected days.
What is a good safety stock buffer for a silo? Set it to at least your supplier's worst-case replenishment lead time plus a margin for weather or rail delays. Three days is light for rail-served minerals; truck-served local material can run leaner.
When should I reorder bulk mineral for a silo? Reorder when days of supply falls to your safety buffer plus lead time. If protected days hits zero, you are inside the buffer and any delivery slip risks a stockout.
Days of supply vs protected days, what is the difference? Days of supply is the raw runway from current tonnage; protected days subtracts the safety buffer to show how much true slack you have before you eat into the floor that covers delivery lead time.
Why does a constant draw-down assumption matter? If you add a shift or ramp throughput, daily draw-down rises and the same tonnage covers fewer days. Recalculate whenever the production rate changes, not just when inventory changes.

Last reviewed 2026-05-12.