A Mumbai buyer once proudly told us he had found a flat at 18,000 rupees per square foot, well below a neighbouring project quoting 22,000. It sounded like a bargain until we asked one question: per square foot of what? His figure was on super built-up area with a heavy loading, while the neighbour quoted on carpet area. Once both were put on the same carpet area basis, the so called bargain was actually the more expensive flat. The lesson is simple and it is worth real money: the area you compare on decides whether a price is cheap or dear.

The short answer. There are three area figures in play. Carpet area is the usable space inside your walls, built-up area adds walls and balconies, and super built-up area adds a share of common spaces and amenities. Under the RERA Act, 2016, builders must quote and sell on carpet area, and the gap between carpet and super built-up, called the loading factor, is generally around 20 to 30 percent. The trade off to watch: a lower per square foot number quoted on super built-up area can hide a higher real cost per usable foot than a higher number quoted on carpet area.

What exactly is RERA carpet area?

Carpet area is the net usable floor area within the walls of your flat. It includes the space you can lay a carpet on and the internal partition walls, but it excludes the external walls, the balcony and verandah, and shared spaces such as lifts, lobbies and staircases outside your unit. In other words, it is the space you actually live in. The RERA definition matters because it gives every buyer and builder the same yardstick, ending years of each project measuring space its own way.

It is worth pausing on what carpet area deliberately leaves out. Balconies and verandahs are excluded from the RERA carpet figure even though you use them, which is why a flat with a large balcony can feel bigger than its carpet number suggests. Some developers quote balcony area separately. When you compare flats, note whether a generous balcony is or is not inside the carpet figure, so you are weighing usable indoor space on a consistent basis across every option rather than being swayed by an open terrace.

This is the figure to anchor on because it is the one you occupy. Two flats with the same super built-up area can offer noticeably different carpet areas depending on how much common space and loading the builder has added, so the carpet number is where real comparison begins.

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

They add layers on top of carpet area, and each layer is space you pay for but do not fully use. Built-up area takes the carpet area and adds the thickness of the external walls and the balcony, so it typically runs somewhere around 15 to 30 percent larger than carpet area. Super built-up area then adds your proportionate share of common spaces, corridors, the lift, the lobby, and amenities such as a clubhouse, gym or pool. It is the largest of the three figures and the one builders historically preferred to quote, because a big denominator makes the per square foot price look small.

None of this means common spaces have no value. A good lobby, working lifts and real amenities are part of what you buy. The point is only that you should know how much of your money is going to your own floor and how much to shared space, and the three figures let you see that split clearly.

What does RERA require builders to do?

The Act made carpet area the mandatory basis for pricing and sale. Under the RERA Act, 2016, it is obligatory for builders to sell property on carpet area, which ended the earlier and often confusing practice of marketing flats on super built-up area. That older practice let a builder quote a low looking per square foot figure by dividing the price across an inflated area. With carpet area as the legal basis, the price in your agreement and the area it is tied to now speak the same language.

You can hold a builder to this. If a sales pitch leads with a per square foot number on super built-up area, that is a signal to ask for the RERA carpet area and the price on that basis before you compare anything. Because carpet area also feeds directly into your stamp duty in cities like Mumbai, getting it right serves you twice, and our guide to Mumbai stamp duty and registration charges shows how the carpet figure flows into the duty you pay.

How do I turn this into a fair price comparison?

Put every option on the same carpet area basis before you judge any of them. Ask each builder for the RERA carpet area and the total price, then divide price by carpet area to get a true per square foot figure. Do that for every shortlisted flat and you can finally compare like with like. The seven steps below make it routine.

1. Ask the builder for the RERA carpet area of the exact flat, in writing.
2. Ask for the total price, including floor rise and any preferential location charge.
3. Divide the total price by the carpet area to get the real per square foot cost.
4. Repeat for every flat you are comparing so all figures are on carpet area.
5. Ask each builder for the loading factor or super built-up area to gauge efficiency.
6. Prefer the flat with the lower true per carpet foot cost, all else being equal.
7. Confirm the carpet area written in your agreement matches the number you were quoted.

This one habit protects you from the most common pricing sleight of hand in the market. It also pairs with location comparisons, since a slightly cheaper suburb can still cost more per usable foot once loading is accounted for, as our Thane versus Kalyan Dombivli end user guide illustrates when read with the carpet math in mind.

How does the loading factor change what I get?

The loading factor decides how much usable space sits behind a super built-up number. It is the extra percentage added to carpet area to reach super built-up area, generally around 20 to 30 percent, though amenity heavy projects can push higher. A flat sold as 1,000 square feet super built-up at 25 percent loading gives you about 800 square feet of carpet, while the same 1,000 super built-up at 40 percent loading gives you closer to 715. Same headline size, very different homes. When two projects quote similar super built-up areas, the one with the lower loading is handing you more of the space you actually live in.

There is no single correct loading factor, since more amenities genuinely cost more space. What matters is that you know the number and price accordingly, rather than paying a premium for loading you did not realise you were buying.

Loading also explains why two flats at the same price can feel so different once you move in. The one with tighter loading gives you more room, more storage and more resale appeal per rupee, because buyers eventually judge a home by how it lives rather than by the brochure figure. Asking for the loading factor early, and treating a vague answer as a yellow flag, is one of the simplest ways to protect the money you are about to commit to a home you will live in for years.

What should a buyer do before signing?

Insist on the carpet area in writing, compute the true per square foot cost on that figure for every option, and check that the carpet area in your final agreement matches what you were sold. Treat any reluctance to share the RERA carpet area as a reason to slow down. When you weigh a specific project, such as Prestige Garden Trails in Mira Road, judge it on price per carpet foot and on its loading factor, not on a super built-up headline. Do that consistently and you will compare homes on the space you will actually live in, which is the only comparison that counts.

Frequently asked questions

What is RERA carpet area?

RERA carpet area is the net usable floor area within the walls of your flat, including internal partition walls but excluding external walls, balconies, verandahs and shared spaces like lifts and lobbies. It is the space you can actually use, and under the RERA Act builders must quote and sell on this figure rather than a larger one.

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

Carpet area is your usable floor space. Built-up area adds the thickness of external walls and balconies, running roughly 15 to 30 percent larger. Super built-up area adds a share of common spaces like corridors, lobbies and amenities, and is the largest of the three. Only carpet area reflects the space you live in.

Are builders allowed to sell on super built-up area?

No. Under the RERA Act, 2016 it is obligatory for builders to sell and price flats on carpet area, ending the older practice of marketing on super built-up area. A price or per square foot figure quoted only on super built-up should be a prompt to ask for the carpet area figure and recompute before you compare.

What is a loading factor and why does it matter?

The loading factor is the extra percentage added to carpet area to reach super built-up area, generally around 20 to 30 percent. A higher loading means you get less usable space for the same super built-up number. Comparing loading factors across projects tells you how much of your money buys walls and shared space versus your own floor.

Last updated 2026-07-17. PropNewz Team.