Loading factor
The percentage gap between carpet area and super built-up area. A 30% loading means you pay for 1,000 sq ft but get ~700 of usable carpet. The higher the loading, the more you're paying for shared space you don't furnish.
The hidden cost
Two flats advertised at the same super built-up area and price can differ by 100+ usable sq ft — a whole small bedroom — depending on loading. Always compare on price per carpet sq ft.