"可用地板面积" can be translated into English as "usable floor area" or "available floor space".
"Usable floor area" emphasizes the area that can actually be utilized or is suitable for use.
"Available floor space" also conveys the idea of the area that is accessible or can be used, though it may sometimes carry a slightly broader or more general connotation.
In most contexts, especially in real estate or architecture, "usable floor area" is a more precise and commonly used term.