What is Min-Max Inventory? Definition & Manufacturing Examples

What is Min-Max Inventory?

Min-max inventory is a replenishment control method where each inventory item has two defined levels: a minimum (reorder point) and a maximum. When the stock quantity drops to or below the minimum level, a replenishment order is placed for the quantity needed to bring the stock back up to the maximum level. The order quantity varies each time based on the current stock level at the time of ordering.

Min-max is one of the oldest and most widely used inventory management methods because of its simplicity. It requires no complex calculations at the time of ordering — the system simply compares current stock to the minimum and calculates the quantity needed to reach the maximum. This makes it particularly effective for managing large numbers of SKUs where more sophisticated methods would be administratively impractical.

The method works best for items with relatively stable demand patterns and consistent lead times. For items with highly variable or seasonal demand, min-max parameters need more frequent adjustment. More sophisticated methods like MRP-driven planning may be better suited for those items.

How Min-Max Inventory Works in Manufacturing

Setting up min-max parameters requires calculating both levels based on demand data and lead times:

Minimum Level (Reorder Point): Min = (Average daily usage × Lead time in days) + Safety stock

The minimum must cover demand during the replenishment lead time plus a safety buffer. If average daily usage is 50 units, lead time is 10 days, and safety stock is 100 units, the minimum is (50 × 10) + 100 = 600 units.

Maximum Level: Max = Min + EOQ or Min + (Average daily usage × Review cycle days)

The maximum should be high enough to cover demand through the next review cycle plus lead time, but not so high that it creates excessive carrying costs. Using the same example with an EOQ of 800 units: Max = 600 + 800 = 1,400 units.

Order Quantity: Order Qty = Maximum - Current stock on hand - Stock on order

This variable order quantity is a key feature of min-max. Unlike a fixed-order-quantity system (where the same amount is ordered every time), min-max adjusts the order size based on current stock levels.

Most ERP systems include min-max functionality as a standard feature. The system automatically generates purchase requisitions or planned production orders when stock drops to the minimum level.

Min-Max Example

A manufacturer of hydraulic fittings uses min-max for brass bar stock:

• Average daily consumption: 30 bars
• Supplier lead time: 14 days
• Safety stock: 90 bars (3 days of demand)
• Minimum = (30 × 14) + 90 = 510 bars
• Maximum = 510 + 450 (EOQ) = 960 bars

On Monday, the warehouse reports 505 bars on hand — below the minimum of 510. The system generates a purchase order for 960 - 505 = 455 bars.

Two weeks later, the shipment arrives when stock is at 85 bars (the safety stock cushioned the remaining demand). After receiving the 455 bars, stock is at 540 bars — below the maximum because consumption continued during lead time. The system does not reorder because 540 exceeds the minimum of 510.

Over a year, this min-max system maintains an average inventory of approximately 735 bars ($44,100 at $60 per bar), with zero stockouts and 12 replenishment orders — a manageable administrative burden.

Why Min-Max Matters for Production Scheduling

Min-max inventory levels directly affect production scheduling because they determine material availability. When the minimum is set too low, stockouts occur and production schedules are disrupted. When the maximum is set too high, excess inventory ties up working capital and warehouse space.

Well-calibrated min-max parameters ensure that materials are available when the scheduler needs them without excessive investment. This is especially important for raw materials and purchased components that have long supplier lead times.

Production scheduling software like Resource Manager DB helps planners coordinate production schedules with material availability. When min-max systems trigger replenishment orders, the scheduler can verify that materials will arrive in time for planned production starts.

Schedulers should also review min-max parameters when production volumes change significantly. A 30% increase in production volume requires corresponding increases in min and max levels to prevent stockouts that disrupt the new schedule.

Related Terms

• Reorder Point — the minimum level in a min-max system that triggers replenishment
• Safety Stock — buffer inventory included in the minimum level calculation
• Economic Order Quantity — the optimal order quantity often used to set the max level

FAQ

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