EOQképlet

The EOQ képlet, or the Economic Order Quantity formula, is a foundational model in inventory management used to determine the optimal order size that minimizes total annual inventory costs. It seeks to balance the fixed cost of placing orders with the variable cost of holding inventory.

The standard formula is Q* = sqrt( (2 D S) / H ), where D is the annual demand in units, S is the fixed cost per purchase order, and H is the annual holding cost per unit (or the holding cost rate times the unit cost). If holding cost is expressed as a rate i of the unit cost C (so H = iC), the formula can also be written as Q* = sqrt( (2 D S) / (i C) ). This quantity represents the optimal order size that minimizes the sum of ordering costs and carrying costs under the model’s assumptions.

Commonly used assumptions include constant and known demand, fixed ordering cost, constant lead time, no stockouts, and instantaneous replenishment, with no quantity discounts. The model is most suitable for steady, predictable demand environments and homogeneous items.

Variants and extensions address practical complexities, such as quantity discounts (to reflect lower unit costs at larger orders), backordering or partial stockouts, and production-order models where inventory arrives over time rather than in a single replenishment. Despite limitations, the EOQ képlet remains a core concept in operations management, guiding procurement policies and inventory planning across industries.