How do you size a buffer for long-lead castings?

Multiply daily usage by supplier lead time to get cycle stock, then add safety stock. That total is the inventory you must hold to ride out the lead time without stocking out.

What is protected days of supply?

It is how many days your current on-hand inventory will cover at the current usage rate. In the example the on-hand protects about 12.83 days.

Why is protected days lower than unprotected days?

Protected days factor in the safety buffer you must keep in reserve, so usable coverage is shorter than the raw on-hand divided by usage — here 12.83 protected versus 14.12 unprotected days.

How much safety stock should I hold on castings?

Enough to cover demand variability and supplier lead-time slip. With long-lead foundry parts that miss schedule often, a 10-25% safety factor over cycle stock is common.

Cycle stock vs safety stock — what is the difference?

Cycle stock covers expected demand during the lead time; safety stock is the extra cushion for variability. Buffer inventory is the two added together.

What happens if supplier lead time increases?

Required buffer rises proportionally. A foundry that stretches from 60 to 90 days forces you to hold 50% more cycle stock or risk idling machining cells.

Oil, Gas & Energy Equipment Manufacturing calculator

Long-lead casting buffer Calculator

Long-lead castings — valve bodies, pump housings, wellhead blocks — can carry supplier lead times measured in weeks or months, and a stockout idles an entire machining cell. This calculator sizes the buffer inventory you must hold to cover demand across that lead time plus a safety margin, and converts your current on-hand into protected days of supply. Materials planners and supply-chain leads in oil and gas equipment plants use it to decide reorder points and to argue for working capital tied up in slow-moving foundry parts. Getting the buffer right is the difference between a smooth machining schedule and an expensive expedite.

What this calculator does

Size the buffer stock for long-lead castings and forgings, such as valve bodies and pump casings, from daily usage, supplier lead time, and a safety stock quantity, so planners can cover the lead time and protect the build schedule.
Use it when setting safety stock for long-lead castings or forgings and you want a buffer based on real usage and lead time.
It computes required casting buffer inventory as lead-time demand plus safety stock, and shows how many days your current on-hand actually protects.

Formula used

Cycle stock = daily usage of castings × supplier lead time
Required casting buffer inventory = cycle stock + safety stock quantity

Inputs explained

Daily usage of castings:
Supplier lead time:
Safety stock quantity:

How to use the result

Use it when setting reorder points for long-lead foundry parts or reviewing whether buffers still match current demand and supplier performance.
It assumes steady daily usage and a stable lead time; lumpy project demand or a foundry that slips schedule will undercut the protection it implies.

Current U.S. benchmarks

Industrial electricity averages 8.66 cents per kWh across the U.S. (EIA, Apr 2026), up 5.5% from a year earlier. Energy-intensive steps carry this directly into unit cost.
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 size a buffer for long-lead castings? Multiply daily usage by supplier lead time to get cycle stock, then add safety stock. That total is the inventory you must hold to ride out the lead time without stocking out.
What is protected days of supply? It is how many days your current on-hand inventory will cover at the current usage rate. In the example the on-hand protects about 12.83 days.
Why is protected days lower than unprotected days? Protected days factor in the safety buffer you must keep in reserve, so usable coverage is shorter than the raw on-hand divided by usage — here 12.83 protected versus 14.12 unprotected days.
How much safety stock should I hold on castings? Enough to cover demand variability and supplier lead-time slip. With long-lead foundry parts that miss schedule often, a 10-25% safety factor over cycle stock is common.
Cycle stock vs safety stock — what is the difference? Cycle stock covers expected demand during the lead time; safety stock is the extra cushion for variability. Buffer inventory is the two added together.

Last reviewed 2026-05-12.