What is Reorder Point? Definition & Manufacturing Examples

What is Reorder Point?

The reorder point (ROP) is the predetermined inventory level at which a replenishment order must be placed to ensure that stock does not run out before the new order arrives. It bridges the gap between current inventory and future demand by accounting for the consumption that will occur during the supplier's lead time, plus a safety stock buffer to protect against variability in both demand and supply.

The reorder point formula is: ROP = (Average daily demand × Lead time in days) + Safety stock

The reorder point is a foundational concept in inventory management. It answers the critical question: "When should I order more?" Combined with economic order quantity (how much to order) or min-max levels, the reorder point creates a complete replenishment system.

Every item in inventory should have a calculated reorder point based on its specific demand rate, lead time, and variability characteristics. Using the same reorder point for all items — or relying on intuition — leads to simultaneous overstocking of some items and stockouts of others.

How Reorder Point Works in Manufacturing

Calculating an effective reorder point requires three inputs:

Average daily demand. This is the average quantity consumed per day, calculated from historical usage data. For manufacturing, this should be based on actual production consumption rather than sales forecasts, since production scheduling determines when materials are needed.

Lead time. The total elapsed time from placing the order to having the material available for production. This includes supplier processing time, manufacturing time (if the supplier builds to order), transit time, receiving and inspection time, and put-away time. Every step in this chain contributes to the lead time.

Safety stock. A buffer quantity that protects against variability in both demand and lead time. If demand is always exactly average and lead times are always exactly as quoted, no safety stock is needed. In reality, both vary — and safety stock absorbs this variability to prevent stockouts.

In an ERP system, reorder points are maintained for each inventory item. When the system's periodic review (or real-time monitoring) detects that on-hand quantity has dropped to or below the ROP, it automatically generates a purchase requisition or planned order.

For items managed by MRP, the reorder point concept is embedded in the MRP logic — net requirements trigger planned orders when projected available inventory drops below the safety stock level.

Reorder Point Example

A manufacturer of precision fasteners consumes nickel alloy wire at the following rate:

• Average daily consumption: 25 kg
• Consumption variability (standard deviation): 5 kg per day
• Supplier lead time: 15 days
• Lead time variability (standard deviation): 2 days
• Desired service level: 95% (z-score = 1.65)

Safety stock = z × √(lead time × demand variance² + average demand² × lead time variance²) = 1.65 × √(15 × 25 + 625 × 4) = 1.65 × √(375 + 2,500) = 1.65 × √2,875 = 1.65 × 53.6 = 88 kg

Reorder point = (25 × 15) + 88 = 375 + 88 = 463 kg

When the nickel alloy wire inventory drops to 463 kg, the system generates a purchase order. The 375 kg covers average demand during the 15-day lead time, and the 88 kg safety stock protects against the combined variability in demand and lead time at a 95% confidence level.

Over a year, this reorder point should prevent stockouts approximately 95% of the time — meaning roughly one stockout event per year on this item. If the manufacturer needs 99% service, they increase the z-score to 2.33, raising safety stock to 125 kg and the ROP to 500 kg.

Why Reorder Point Matters for Production Scheduling

The reorder point is one of the most direct connections between inventory management and production scheduling. When the ROP is correctly set, materials arrive before they are needed — and the production schedule runs smoothly. When the ROP is wrong, materials arrive late (or not at all), and the scheduler must react with expediting, job resequencing, or partial shipments.

Production scheduling software like Resource Manager DB provides visibility into upcoming material requirements, allowing planners to verify that reorder points will trigger orders in time for scheduled production starts. When production schedules change, the effective demand rate changes — and reorder points may need adjustment.

Schedulers should collaborate with inventory management to ensure that ROPs reflect current production rates, not historical averages that may be outdated.

Related Terms

• Safety Stock — the buffer component within the reorder point calculation
• Economic Order Quantity — determines how much to order when the reorder point is reached
• Stockout — the condition that occurs when reorder points fail to trigger timely replenishment

FAQ

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This term is part of our Manufacturing & Production Scheduling Glossary. Learn more about inventory management, scheduling, and manufacturing terminology.