Now the calculation : Lets take your example, if carpet area is 600 sq ft. Then the super build up area would be :- Lets assume the ratio is 75:25. Means carpet area is 75% of super built up area. super built up area = 600 + 25% of 600 = 600 + 150 = 750 SQ FT So the carpet area of 1200 sq-ft house will be 1200*75/100= 900 sq-ft.
Built up Area is the carpet area plus the thickness of outer walls and the balcony.
Super Built Up Area is the built up area plus proportionate area of common areas such as the lobby, lifts shaft, stairs, etc. Sometimes it may also include the common areas such, swimming pool, garden, clubhouse, etc.
Generally carpet area is around (70 to 80)% of super built up area. But note that this percentage varies from project to project and builder to builder. When carpet area is 40*30 i.e 1200 sq-ft. then built up area will be 25% of 1200+1200=1500 sq-ft.