The gross floor area below ground in any built object is the total floor area within that object, including usage areas as well as mechanical, storage, transportation, and other areas (but not including columns, walls, and other built-up spaces), which is on any floor counted as an underground floor.

The total gross floor area of any object equals the gross floor area below ground + the gross floor area above ground.

An area is only comparable alongside the standard it was measured to. National measuring codes differ over balconies, atrium voids and shafts, so two published figures for one building can both be correct.

A figure that covers a complex rather than a single building is a different measurement again. Where a tower shares a podium, the record has to say whether the podium is inside the figure.