Every Mumbai flat hunter eventually has the same experience. The listing says 1,050 sq ft. You walk in, look around the living room, and quietly wonder where the other few hundred square feet went. Nobody has stolen them. They were simply never yours to live in. They were counted in the lift lobby, the staircase, the wall between you and the neighbour, and a clubhouse you may use twice a year.
Understanding how area is described is the single most useful skill a buyer or tenant in this city can develop. It is also the one that listings, brokers and hoardings are least keen to teach you.
Three numbers for one flat
Carpet area is the usable floor space inside your flat. Under the Real Estate (Regulation and Development) Act, 2016, it is defined as the net usable floor area of an apartment, excluding the area covered by the external walls, service shafts, exclusive balconies or verandahs and exclusive open terraces, but including the area covered by the internal partition walls. In plain terms: the floor you can put furniture on, plus the thickness of the walls between your own rooms.
Built-up area is a looser, older term. It usually means carpet area plus the external walls, and often the balcony and similar spaces that belong exclusively to the flat. There is no single statutory definition that everyone follows, which is exactly the problem.
Super built-up area, sometimes called saleable area, takes the built-up area and adds a proportionate share of the building's common spaces: lobbies, staircases, lift wells, corridors, sometimes the gym, the clubhouse and the podium garden. It is a number that describes your share of the building, not your home.
The gap between the first and the last is called loading. If a flat has a carpet area of 700 sq ft and is sold as 1,050 sq ft super built-up, the loading is 50 per cent. I have seen listings where it is considerably higher, particularly in towers with generous amenities, and older buildings where it is modest. The point is not that loading is wicked. Common areas cost money to build. The point is that you cannot compare two flats until you know how much of each number is air.
What RERA changed
Before RERA, developers could, and many did, price flats on super built-up area with loading figures that varied project to project and were rarely disclosed. Two flats advertised at the same size could differ by a hundred square feet or more of real living space.
RERA made carpet area the legal unit of sale. A developer selling a flat in a registered project must state its carpet area in the agreement for sale, and the price is expressed against that carpet area. In Maharashtra, projects must be registered with MahaRERA, and the project's registration page will usually carry the approved plans and a breakdown of apartment types and their carpet areas. It is worth checking that page against whatever the sales office hands you.
Two caveats. First, the law governs the agreement, not the hoarding or the WhatsApp forward. Marketing material and brokers still quote super built-up figures, often without saying so. Second, RERA applies to new projects that fall under it. In the resale market, and in rentals, the old vocabulary survives almost untouched. A broker describing a flat in a 1980s building in Khar as "900 square feet" might mean any of the three, and may not know which.
Balconies, flower beds and other grey areas
Mumbai flats come with their own vocabulary of extras: enclosed balconies, flower beds, niches, deck areas, dry balconies for the washing machine. Under the RERA definition, exclusive balconies are excluded from carpet area and are typically disclosed separately. In older buildings, however, many balconies were enclosed long ago and have quietly become part of a bedroom. They feel like carpet area. On paper they may not be, and an enclosure may not have been approved at all.
This matters when you buy, because the society's records, the original approved plan and the sale deed may all describe a smaller flat than the one you are standing in. It also matters when a building goes for redevelopment, because entitlements are usually calculated on the documented carpet area, not on the space you have been using. If the extra space was never regularised, you should not pay for it as though it were.
Comparing prices honestly
Once you know the carpet area, the rest is arithmetic. Here is the method I use.
- Get the carpet area in writing. For a new project, it is in the agreement and on MahaRERA. For resale, ask for the previous agreement, the society's share certificate and any approved plan, and measure it yourself if in doubt.
- Convert every asking price to a price per sq ft of carpet area. If a flat is quoted at ₹30,000 per sq ft on 1,050 sq ft of super built-up area, the total is roughly ₹3.15 crore. If the carpet area is 700 sq ft, you are really paying about ₹45,000 per sq ft of carpet. That is the number to compare.
- Add the unavoidable extras. Parking, floor-rise charges, club membership and development charges can be quoted separately. Fold them into the total before you divide.
- Separately note what the loading buys you. A higher loading in a building with a well-run gym, a real garden and good lifts is not the same as a higher loading on a corridor that smells of paint.
- Compare against the government's valuation. The ready reckoner rate for the area, published by the state, gives you a floor below which stamp duty will not go and a rough sense of how the neighbourhood is assessed. You can find it through IGR Maharashtra.
A useful habit is to ask one blunt question at the start of every conversation: "Is that carpet?" Good brokers answer immediately. The ones who hesitate have told you something too.
Measuring for yourself
For resale flats, I recommend taking a tape measure. It feels faintly absurd, standing in a stranger's bedroom measuring the wall, but it takes twenty minutes and removes an enormous amount of uncertainty. Measure each room wall to wall, add them up, and add a modest allowance for internal walls. You will not match the legal definition to the last square foot, but you will know whether "900" means 650 or 850.
A friend in Dadar did exactly this before buying and found the flat was a little under two-thirds of the number in the listing. The seller had not lied, exactly. The figure had been passed down from an old brochure. But it meant the per-sq-ft price was far above the lane's going rate, and the negotiation that followed was much shorter than it would otherwise have been.
The number that matters
Mumbai sells its homes by the square foot because space is the one thing the city cannot manufacture. That makes it all the more important to know which square feet you are buying. RERA has given buyers of new flats a clear legal measure, and it would be a waste not to use it everywhere, including in the resale and rental markets where no law forces anyone to.
So read the listing, then ignore the headline figure until you have converted it. The carpet area is the home. Everything else is the building, and while you will certainly pay for the building, you should know exactly how much of it you are paying for.
