The foundation and relatively fixed storage capacity in a store is directly a consequence of the layout and equipment (rack, shelving, etc.). To optimize the storage capacity of each store requires an understanding of the unique mix of inventory that will be stored in it, and the level of activity expected within it.
To calculate the storage capacity of a store we develop the ratio of the cubic storage capacity of the storage aids or storage space (where materials are stored on the floor), divided by the total cubic volume of the portion of the building occupied by the storage, (or the inverse). The following measures are the elements for developing the ratio. To develop the volume of the building we measure the dimensions of the inside of the building; the length, width, (less the offices, rest rooms, etc.), and maximum stack height. This is the total building space we can work with. Based on the characteristics of the inventory and the material handling (cranes, ASRS, etc.) and storage (sprinklers, placement of lighting, etc.) requirements we can develop several layout options within this space.
For each storage area in a layout we calculate a storage capacity, based on the drawings of the layout, and add them together. This is the total, theoretical storage capacity. It is theoretical because, for example, efficient material handling usually requires that a pallet load not fill the allocated space (on the floor or in selective rack, etc.) completely, so that the pallet loads can be easily moved into and out of the storage position. So for pallet rack we use the dimensions of the rack structure including the area above the top set of beams and calculate a cubic volume.
Similarly for shelving we calculate the internal volume of the shelving section. This is not a precise calculation, but the differences between various alternative layouts typically does not justify spending a lot of time getting exact measurements. Most stores usually utilize between 22% and 27% of the store space as storage. This ratio provides the way to help us better understand the importance and tradeoffs in the number and width of aisles, the orientation of the aisles, the size and orientation of the rack and shelving,
what is the building clear height that can be used with the existing fire control system, and begin to help us understand the functional and financial consequences of the many other available options, including selective rack, two deep selective rack, push back, drive through, storage and retrieval systems, floor storage, flow rack, etc. Evaluating alternatives requires us to better understand the nature of the inventory to be stored in them and how the warehouse will be used. As we consider alternatives, we can begin to see how important the layout can be and how layout and choice of storage aid addresses only half of the issue.