Usable building area has many purposes
Warehouses often include offices, washrooms, lunch areas, first-aid facilities, accessible routes, mechanical rooms and other support areas. These should be excluded from storage-capacity calculations unless their use is formally changed and permitted.
Accessibility requirements vary
Accessible routes, parking, entrances, washrooms and other requirements differ by jurisdiction and building use. Capacity calculations should never assume that an apparently open area can be converted to storage.
Changes can trigger review
A renovation, mezzanine, office addition or change in use may create building, accessibility, fire or occupational-safety requirements. Confirm requirements before relying on the proposed area in a business case.
Plan with a facility drawing
A current, verified drawing with clearly labelled non-storage areas provides a better capacity baseline than multiplying the building's advertised length and width.
Practical questions
Should I use one utilization percentage for every warehouse?
No. Inventory profile, storage system, seasonality, staging demand, handling equipment and workflow can make the same percentage perform very differently in two facilities.
Can this guide be used to approve a rack or building change?
No. It is a planning resource. Structural, fire, building, accessibility and workplace-safety requirements must be established for the actual facility by the appropriate qualified parties and authorities.