Two Mumbai buyers compared what looked like the same 1,000 square foot flat in adjoining towers. One was quoted 1,000 square feet of carpet area, the other 1,000 square feet of super built-up area. They cost almost the same per square foot on paper, yet the first home had nearly a third more usable space inside the front door. The difference was not the builder being generous or stingy; it was the area measure each brochure quietly used. For a buyer, learning to read carpet area against super built-up area is the difference between comparing homes fairly and paying for space you will never stand in.

The short answer. Under RERA, builders must quote and price a flat on its carpet area, the net usable floor space within your walls, not the super built-up area that loads in a share of lobbies, lifts and amenities. The gap between the two is the loading factor, commonly 25 to 40 percent and sometimes more. The trade off to watch is that a low headline price per square foot can hide a high loading, so always compare homes on price per carpet square foot, and read the carpet figure in your MahaRERA registered agreement, not the marketing area.

What is carpet area under RERA?

Carpet area under RERA is the net usable floor area inside your apartment. The definition in the RERA Act describes it as the net usable floor area of an apartment, excluding the area covered by external walls, areas under service shafts, and the exclusive balcony, verandah or open terrace area, but including the area covered by the internal partition walls of the apartment. In plain terms, it is the space you could actually lay a carpet on, plus the thickness of the internal walls, and nothing that sits outside your front door.

This matters because carpet area is the one measure that cannot be inflated by adding shared spaces. Before RERA, buyers routinely paid for super built-up area that bundled in a share of corridors, the club house and the lift core, with no standard rule for how much. RERA replaced that with a single defined figure that every registered project must disclose, which is why the carpet area is the number you should anchor every comparison to.

How do carpet, built-up and super built-up area differ?

They differ by how much beyond your usable floor they include. Carpet area is the usable space within your walls. Built-up area adds the internal walls and the balcony, and, as developer handbooks note, is typically 10 to 20 percent larger than carpet. Super built-up area adds a share of common areas such as lifts, staircases and lobbies on top of that, and is generally another 25 to 30 percent larger again, which is how a modest usable space ends up marketed as a much bigger number. The table below sets out the three, plus the loading that stacks common space onto your carpet.

Because each layer is larger than the last, the same flat can be described in three very different square foot figures. A brochure that leads with the largest of them is not lying, but it is showing you the number least useful for judging what you get.

Does RERA make builders price flats on carpet area?

Yes, RERA requires developers to disclose and sell on carpet area rather than super built-up area. Since the Act came into force, promoters are bound to state the carpet area and to base the price on it, so that a buyer pays for usable space rather than an undefined share of common areas. MahaRERA, the Maharashtra authority, requires promoters to disclose project details including carpet area and inventory in a consistent format on the registered project record.

This does not stop a sales team from also quoting a super built-up figure or a price per super built-up square foot in conversation. It does mean the binding number in your registered agreement should be the carpet area, so insist that the figure you negotiate on and the figure in the agreement are the same carpet area, expressed the same way.

What is the loading factor and how do I calculate it?

The loading factor is the gap between the super built-up area and the carpet area, expressed as a percentage of carpet. If a flat has a carpet area of 700 square feet and is marketed as 1,000 super built-up square feet, the loading is 300 square feet, or about 43 percent. A higher loading means more of what you pay for is shared space rather than your own floor. There is no single legal cap on loading, so it varies widely between projects, which is exactly why comparing two flats on their super built-up price can be misleading.

To calculate it yourself, take the super built-up figure, subtract the carpet area, and divide the result by the carpet area. Do this for every flat you shortlist. Two homes at the same price per super built-up square foot can hide very different carpet areas, and the one with the lower loading gives you more usable space for the same money.

What happens if the delivered carpet area is less than promised?

If the carpet area handed over is smaller than the agreement, RERA entitles you to a refund of the excess amount you paid, with interest. The framework and the standard sale agreement provide that where the actual carpet area falls short of what was committed, the promoter must return the proportionate amount for the shortfall together with interest, generally within a defined period. This is a genuine buyer protection, but you can only use it if the agreement records a specific carpet area to measure the delivered flat against.

So the practical step is to make sure the exact carpet area is written into your registered agreement, ideally with a room by room breakdown. A vague area clause weakens your ability to claim a refund later. For how these clauses are framed, our guide to the MahaRERA model agreement for sale clauses walks through what the agreement should contain.

How do I check the carpet area before I buy?

Check the carpet area against the MahaRERA registered project record and the sale agreement, not the brochure. The authority publishes registered project details, and the carpet area disclosed there is the figure the promoter has committed to the regulator. Cross check that against the area in your draft agreement and against what the sales team has quoted; all three should match. Our explainer on how to verify a project on the MahaRERA portal shows where these disclosures sit.

You can look up the official record on the MahaRERA portal at maharera.maharashtra.gov.in, which is the reference that matters if the brochure and the agreement disagree. If a promoter is reluctant to put the carpet area in writing or to reconcile it with the registered disclosure, treat that as a warning rather than a detail to settle later.

What mistakes cost Mumbai buyers when comparing flats?

The most expensive mistake is comparing flats on the wrong area measure. Buyers who compare price per super built-up square foot across projects with different loadings end up paying more per usable foot without realising it. Others accept a carpet area verbally but let the agreement record only a super built-up or saleable figure, which weakens any later claim over a shortfall. Use the checklist below to keep every comparison on the same, honest basis.

1. Ask for the RERA carpet area in writing, not the super built-up or saleable area.
2. Confirm the carpet figure matches the MahaRERA registered project disclosure.
3. Calculate the loading by comparing the super built-up quoted with the carpet area.
4. Compare shortlisted flats on price per carpet square foot, not per super built-up foot.
5. Check the sale agreement states the price is set on the carpet area.
6. Ask for a room by room carpet area breakdown wherever the builder can provide it.
7. Keep the agreement clause on area shortfall and confirm the delivered carpet area at possession.

Do all seven and you will compare homes on what you actually get to use, which is the only fair way to judge value between two Mumbai towers.

Frequently asked questions

What is carpet area as per RERA?

Carpet area under RERA is the net usable floor area within your apartment. It excludes external walls, service shafts, and the exclusive balcony, verandah or open terrace, but includes the internal partition walls. It is the space you can actually use, and RERA requires developers to disclose and price flats on this figure rather than super built-up area.

What is the loading factor on a Mumbai flat?

The loading factor is the gap between the super built-up area and the carpet area, shown as a percentage of carpet. If carpet is 700 square feet and super built-up is 1,000, the loading is about 43 percent. Loading is commonly 25 to 40 percent and sometimes higher, and there is no fixed legal cap, so it varies between projects.

Can a builder still sell on super built-up area?

A sales team may quote a super built-up figure in conversation, but under RERA the binding sale must be based on carpet area, and the registered agreement should record that carpet area. Insist that the number you negotiate on and the number in the agreement are the same carpet area, so you are not paying for undefined shared space.

What if my delivered flat has less carpet area than promised?

If the delivered carpet area is smaller than your registered agreement states, RERA entitles you to a refund of the proportionate excess you paid, with interest, usually within a defined period. This protection works only if the agreement records a specific carpet area, so make sure the exact figure is written in before you sign.

Last updated 2026-07-12. PropNewz Team.