storage capacity
The total volume within a built object allocated to its primary storage areas.
The storage capacity of a built object is the total amount of room available for storage of whichever objects or materials are normally stored there, expressed in cubic units of volume. This does not include storage of materials for supporting utilities, such as water or natural gas, unless the structure's main purpose is for the storage of those materials. This field may be used for either bulk commodity storage or for shelf storage (and similar warehouse-type storage).
This measures room for contents and not enclosed building space. A warehouse has a storage volume smaller than its architectural volume, because aisles, offices and the space above the racking are not storage.
The figure belongs to the installation rather than the building. Replacing racking or tanks changes it while the structure stays as it was.