Comparing handling and space costs for various types of stacking methods

In stacking facilities where unit loads are stacked in multiple tiers, as the number of tiers increases, the space consumption per unit load decreases; at the same time, the expected number of relocations during retrieval operations increases. This study derives formulas for estimating the expected number of relocations for retrieving a unit load from various types of stacks with different combinations of the number of rows, number of columns, and number of tiers. Based on the derived formulas, the handling cost and the space cost of the different types of stacks are compared with each other.