Determining a lot size to order or to produce is an important issue in inventory management and a materials requirements plan. EOQ can be used to determine lot size or there are a number of specific plans to use depending on your industry, product, and cost structure. However, in many instances lot sizes may be determined for you. For example, you could go to the store and attempt to purchase one M&M, but the cashier most likely will charge you for the entire package. M&M's come in certain lot sizes, such as small bags, medium bags, or large bags.