EOQ is a formula that calculates the optimal order quantity to minimize total inventory costs, including ordering costs and holding costs. It's important because it helps businesses balance the cost of ordering frequently (high ordering costs) against the cost of holding large inventories (high holding costs), ultimately reducing total inventory expenses.

The EOQ formula is √(2DS/H), where D = annual demand, S = ordering cost per order, and H = holding cost per unit per year. This formula finds the sweet spot where ordering costs equal holding costs, minimizing total cost. The square root relationship means small changes in parameters have diminishing effects on the optimal quantity.

Reorder point is the inventory level that triggers a new order, calculated as lead time demand plus safety stock. Safety stock is a buffer inventory held to protect against demand variability and supply delays. The reorder point ensures you order before running out, while safety stock provides protection against uncertainties during lead time.

Service level represents the probability of not running out of stock during lead time. Higher service levels (95-99%) are appropriate for critical items, high-value customers, or when stockouts are very costly. Lower service levels (85-95%) may be acceptable for less critical items. Consider the cost of stockouts versus the cost of carrying extra safety stock.

EOQ assumes constant demand, fixed ordering and holding costs, instant delivery, no quantity discounts, and independent item demand. In reality, demand varies, costs may change, and suppliers offer discounts. Despite these limitations, EOQ provides a valuable baseline for inventory management and can be adapted with modifications for more complex scenarios.