Once the number of storage locations is known, the optimal size of the storage zone can be determined. It should be observed that a solution to this problem strongly depends on the selected warehouse layout, on the kind of storage and material-handling systems used, which affect the storage and retrieval times of the products in warehouse. The problem will therefore be solved for a specific warehouse layout, even though the approach followed remains valid in general, in the sense that it can be easily extended to other cases. In particular, it is supposed that the warehouse layout is of the flow-through type with a single entrance and a single exit for the storage zone, that the material-handling systems are without mobility constraints and that conventional racks are used in the storage zone with the layout shown in Figure 5.24. The case in which the storage zone is served by stacker cranes will be illustrated in Section 5.6.