How do you calculate inventory coverage in days?

Divide on-hand inventory by average daily usage, adjusted for your safety factor and lead time. In the example, 1,200 units against 85 units/day yields about 12.83 protected days versus 14.12 unprotected days.

What's the difference between protected and unprotected days?

Unprotected days (14.12) is raw inventory divided by usage. Protected days (12.83) applies the safety factor so you're comparing coverage against lead-time risk, giving a more conservative runway you can actually rely on.

What is a good days-of-supply for specialty barrier resin?

It depends on lead time — you want coverage comfortably above supplier lead time. If EVOH lead time is 10 days, the 12.83 protected days here gives only a thin buffer, so most planners would hold more.

How does lead time factor into coverage?

Coverage must exceed lead time to avoid a stockout while a replenishment order is in transit. If protected days fall below lead time, you're already too late to reorder without risking a line-down.

Why hold safety stock for film and membrane materials?

To absorb usage spikes and supplier variability. Barrier resins have volatile lead times, so the safety factor converts raw days (14.12) into a more defensible protected figure (12.83) that plans for the bad case.

How do I set a reorder point from coverage days?

Reorder when protected days-of-supply approach your supplier lead time plus a review buffer. Working backward from the 85 units/day usage, multiply lead time in days by daily usage to get the reorder quantity in units.

Specialty Films, Membranes & Barrier Materials calculator

Inventory Coverage Calculator

Inventory Coverage tells a film or membrane operation how many days its on-hand roll stock or resin will last, and whether that cushion covers replenishment lead time. Specialty barrier resins like EVOH and specialty tie-layers often carry long, volatile lead times, so running lean risks a line-down event while running heavy ties up cash in cold storage. Materials planners and buyers use days-of-supply to time reorders and set safety stock. It converts raw inventory counts into the language operations actually plans in — days of runway.

What this calculator does

Estimate inventory coverage for specialty films, membranes and barrier materials using production-ready inputs so teams can plan replenishment and safety stock using actual usage and lead time.
Use it when inventory coverage in specialty films, membranes and barrier materials is being sized for a buffer or safety stock review.
It computes protected days of supply from on-hand inventory, factoring daily usage, lead time, and a safety-stock adjustment, and shows the unprotected days for comparison.

Formula used

Inventory coverage cycle stock = inventory coverage daily usage × inventory coverage lead time
Required inventory coverage inventory = cycle stock + inventory coverage safety stock

Inputs explained

Average daily film usage:
Replenishment lead time:
Safety stock multiplier:

How to use the result

Use it when setting reorder points or reviewing whether current stock of a critical resin or roll SKU covers supplier lead time.
It assumes steady average daily usage; a demand spike or a batch build for a long run will burn the coverage faster than the flat rate implies.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Global copper trades at $13,484 per tonne (IMF via FRED, May 2026), up 41.5% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.

Common questions

How do you calculate inventory coverage in days? Divide on-hand inventory by average daily usage, adjusted for your safety factor and lead time. In the example, 1,200 units against 85 units/day yields about 12.83 protected days versus 14.12 unprotected days.
What's the difference between protected and unprotected days? Unprotected days (14.12) is raw inventory divided by usage. Protected days (12.83) applies the safety factor so you're comparing coverage against lead-time risk, giving a more conservative runway you can actually rely on.
What is a good days-of-supply for specialty barrier resin? It depends on lead time — you want coverage comfortably above supplier lead time. If EVOH lead time is 10 days, the 12.83 protected days here gives only a thin buffer, so most planners would hold more.
How does lead time factor into coverage? Coverage must exceed lead time to avoid a stockout while a replenishment order is in transit. If protected days fall below lead time, you're already too late to reorder without risking a line-down.
Why hold safety stock for film and membrane materials? To absorb usage spikes and supplier variability. Barrier resins have volatile lead times, so the safety factor converts raw days (14.12) into a more defensible protected figure (12.83) that plans for the bad case.

Last reviewed 2026-05-12.