The Three Areas Defined
Carpet area (RERA) is the net floor area of the apartment you can actually walk on — measured from internal wall to internal wall. It excludes the thickness of external walls but includes internal walls and any net balcony/terrace area. This is the number RERA mandates for all sale agreements since 2017.
Built-up area adds to carpet area the external wall thickness (typically 9–12 inches per wall) and any uncovered balconies or terraces. The ratio of carpet area to built-up area in Ahmedabad's luxury buildings is typically 85–90% — meaning a 2,500 sq.ft. BUA apartment has ~2,125–2,250 sq.ft. of actual carpet area.
Super built-up area (also called 'saleable area' pre-RERA) further adds each buyer's proportionate share of common areas: lift shafts, lobby, staircases, clubhouse, gym, and sometimes even parking structure. SBA can be 120–140% of carpet area — meaning a 3,000 sq.ft. SBA apartment might have only 2,100–2,500 sq.ft. of usable carpet area.
How This Affects Your Purchase
Post-RERA, all sale agreements in Gujarat must use carpet area as the base. However, developers often quote SBA in their marketing materials to make the apartment appear larger. Always insist on the carpet area figure and calculate the price per sq.ft. of carpet area — not SBA — before comparing two properties.
In Ahmedabad's luxury segment, the efficiency ratio (carpet area ÷ SBA) varies significantly by developer and project. Well-designed buildings with larger floor plates can achieve 80–85% efficiency. Older buildings with excessive common areas may be as low as 70–72%. A 72% efficiency building at ₹8,000/SBA delivers ₹11,100/carpet area — less efficient than it appears.
