A buyer comparing two towers in Chandivali did the sensible thing and lined up the price per square foot. One quoted 19,500 rupees a square foot, the other 21,000. The cheaper one looked like the obvious pick. Then her broker asked a question that changed the maths. What area was each price quoted on? The cheaper tower was priced on super built-up area with a heavy loading, while the pricier one was priced closer to carpet. Once she recomputed both on the space she could actually use, the ranking flipped. In Mumbai, where loading can be enormous, the area you are quoted matters as much as the price.

The short answer. Under RERA, a builder must quote the sale price and register the conveyance on carpet area, the net usable space inside your flat, not on super built-up area. Carpet area excludes external walls, shafts, balconies and common areas, while super built-up loads in a share of lobbies, lifts and amenities. In Mumbai, that loading often runs 40 to 50 percent. The trade off to understand is that a low per square foot number quoted on super built-up can be more expensive per usable foot than a higher number quoted on carpet, so always compare like for like.

What does RERA say I should pay for?

RERA requires that the sale price and the conveyance deed be based on carpet area rather than super built-up area, so that a buyer pays for usable living space. This is one of the most important protections the 2016 law brought in, because before it, builders routinely quoted and sold on super built-up area, which is a larger and looser number. According to this explainer on RERA carpet area, the law mandates carpet area as the basis for pricing and the registered deed. For a Mumbai buyer this means you are entitled to see the carpet area clearly stated, and you should insist on it, because that is the figure your money is legally meant to buy.

What exactly is carpet area?

Carpet area is the net usable floor area of your flat, measured inside the walls. Under Section 2k of RERA it excludes the area covered by external walls, areas under service shafts, exclusive balcony or verandah area, and exclusive open terrace area, while it includes the area covered by the internal partition walls of the apartment. In plain terms it is the space you can lay a carpet on, room by room, plus the internal walls. It takes in your bedrooms, living room, kitchen, bathrooms and internal passages, and leaves out lobbies, staircases, lifts, ducts and the balcony. When a builder shows you a number, ask specifically whether it is the RERA carpet area, because that is the only figure defined and protected by law. A useful habit is to write the carpet area, and the area basis, on top of every cost sheet you collect. Sales teams sometimes move between figures within a single conversation, quoting a small rate on the large area and a large size on the small area, and the only defence is to pin down which number goes with which basis before you let any of it influence your decision. If a salesperson resists giving you a plain carpet figure in writing, treat that reluctance itself as information.

What is super built-up area and the loading factor?

Super built-up area is carpet area plus a proportionate share of common spaces such as lobbies, staircases, lift wells and amenities, and the gap between the two is the loading factor. The loading factor is calculated as the super built-up area minus the carpet area, divided by the carpet area, expressed as a percentage. A loading of 30 percent means the super built-up area is 30 percent larger than the space you can actually use. In Mumbai, because land is scarce and towers pack in shared facilities, loading often runs at 40 to 50 percent, as the same guide notes. That is far higher than in many other cities, which is exactly why the area basis deserves close attention here.

Why does loading matter to my per square foot cost?

Loading matters because it decides how much usable space your money buys. A price quoted on super built-up area spreads your rupees across space you cannot use, so the effective cost per usable square foot is higher than the sticker suggests. The table below takes a flat with 700 square feet of carpet area and shows how the super built-up figure and the effective cost per usable square foot climb as loading rises, assuming a quote of 20,000 rupees per square foot on super built-up area. The pattern is stark. The same headline rate becomes a very different real cost once you convert it to carpet, and comparing two flats without doing this conversion is comparing nothing at all.

Use this seven step order to compare flats honestly on area.

1. Ask each builder for the RERA carpet area of the specific flat in writing.
2. Ask separately for the super built-up area so you can work out the loading factor.
3. Calculate loading as super built-up minus carpet, divided by carpet, as a percentage.
4. Convert every quote to a cost per carpet square foot before you compare options.
5. Cross check the carpet area against the RERA registered project disclosures.
6. Confirm the price and the draft agreement are both stated on carpet area.
7. Read the clause on how a change in carpet area at possession will be handled.

How do I check the carpet area before I buy?

Check it in three places and make sure they agree. First, the builder should state the carpet area in the cost sheet and the draft agreement for sale. Second, the project's RERA registration carries disclosures you can verify independently, which our MahaRERA verification guide walks through. Third, the floor plan should let you sanity check that the stated carpet area is consistent with the room sizes. If the cost sheet quietly uses super built-up area while the agreement uses carpet, that mismatch is worth questioning. For a deeper look at how carpet, built-up and super built-up differ, our area concepts guide breaks down each term. One more check is worth doing at the show flat itself. A sample flat is sometimes built slightly larger than the unit you are buying, or furnished to make rooms feel more spacious than the carpet figure suggests. Carry the stated carpet area with you and mentally map it against the rooms you walk through, so the number on paper and the space in front of you tell the same story before you decide.

What if the carpet area changes at possession?

Sometimes the final carpet area at possession differs slightly from what was promised, and your agreement should say how that is handled. A well drafted agreement for sale sets out what happens if the carpet area increases or decreases when the flat is finished, typically adjusting the price up or down within limits and refunding you for any meaningful shortfall. Before you sign, read this clause carefully rather than skimming it, because it protects you against paying for space that never materialised. If the clause is vague or missing, raise it with the builder and your advocate. A change in area is not automatically a problem, but the absence of a clear, fair mechanism to deal with it is a gap you should close before committing. It is worth remembering why this clause exists at all. A flat is often booked years before it is finished, and small design or construction changes can nudge the final carpet area in either direction. A fair agreement treats that possibility openly, adjusting the consideration in proportion and returning money to you if the space shrinks. What you want to avoid is a one sided clause that lets the builder charge you for any increase but stays silent on a decrease. Reading it closely now, with a lawyer, costs you an hour and can save you lakhs at possession.

Does RERA require builders to sell on carpet area?

Yes. RERA requires that the sale price and the conveyance deed be based on carpet area rather than super built-up area, so you pay for usable space. This was a major protection introduced by the 2016 law, because builders previously quoted on the larger super built-up figure. Insist on seeing the RERA carpet area stated in the cost sheet.

What is the difference between carpet area and super built-up area?

Carpet area is the net usable space inside your flat, measured within the walls and excluding common areas. Super built-up area adds a proportionate share of lobbies, lifts, staircases and amenities on top. The gap between them is the loading factor. In Mumbai, loading often runs 40 to 50 percent, so the super built-up figure can be far larger than the space you actually use.

What is a loading factor and what is normal in Mumbai?

The loading factor is the super built-up area minus the carpet area, divided by the carpet area, shown as a percentage. It measures how much common area is loaded onto your usable space. In many cities loading sits around 20 to 30 percent, but in high density Mumbai towers it commonly reaches 40 to 50 percent.

How do I compare two flats priced differently on area?

Convert both to a cost per carpet square foot before comparing. Ask each builder for the RERA carpet area and the super built-up area, work out the loading, and divide the total price by the carpet area. A low headline rate on super built-up area can cost more per usable foot than a higher rate quoted on carpet.

RERA rules and their application can evolve, so confirm the current position and the project's disclosures on the official MahaRERA portal, and have your advocate review the agreement for sale. This guide is buyer education and not legal advice.

Last updated 2026-08-25. PropNewz Team.