In floor area calculations, which dimensions may be used?

• A. Inside dimensions.
• B. Outside dimensions.
• C. Either Inside or Outside dimensions.
• D. Neither Inside nor Outside dimensions.

Answer: (C)

In floor area calculations, you choose the boundary that defines what you’re measuring, and you can use either the inside faces of the walls or the outside faces. Using inside dimensions gives you the usable, net floor space (the area people can actually occupy or use), while using outside dimensions gives the building’s footprint or gross floor area, including wall thickness. Both are valid, but the key is to pick one convention and stick with it throughout the calculation and any related documentation. If you have drawings or a project spec, follow the defined convention there; otherwise, choose inside or outside depending on whether you’re calculating usable area or overall footprint, and clearly state that choice so the result is clear and comparable. The difference between the two amounts will be the wall thickness area that is included or excluded, which is why consistency matters.