A young couple booking their first flat in Mulund were shown a bright show home and a brochure that said 1150 square feet. When they visited the finished apartment months later, it felt smaller than they remembered, and it was. The usable space inside their walls was closer to 800 square feet. Nothing illegal had happened. The brochure had quoted a larger measure that included walls, a share of the lobby, and the lift shaft. The number that described the floor they could actually furnish and live on had a different name, and it is the one the law now puts first. That number is the carpet area.

The short answer. Carpet area is the net usable floor area inside your flat, and under the real estate law known as RERA, builders must quote the price on carpet area rather than on the larger super built up figure. The trade off to understand is that carpet area looks smaller than the numbers buyers are used to seeing, but it is the honest one. A flat advertised for years as 1150 square feet super built up might carry a RERA carpet area of only around 800 square feet, and knowing that gap is how a Mumbai buyer compares two flats fairly.

The definition sits in Section 2(k) of the Real Estate (Regulation and Development) Act 2016, reproduced by legal explainers such as TaxGuru. Here is what it means when you are choosing a home.

What exactly is carpet area under RERA?

Carpet area is the net usable floor area of an apartment, and the law defines it precisely. Under Section 2(k), carpet area is the net usable floor area of an apartment, excluding the area covered by the external walls, areas under services shafts, exclusive balcony or verandah area, and exclusive open terrace area, but including 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 to room, plus the internal walls that divide those rooms, and nothing beyond your front door.

So your bedrooms, living and dining rooms, kitchen, bathrooms, and any internal passage all count. The thick external walls do not, the service shafts do not, and your balcony and any private terrace are measured separately rather than folded into the carpet figure. This is the number that tells you how much home you are really getting.

How is carpet area different from built up and super built up?

The three terms describe steadily larger areas, and only one is standardised. Built up area adds the thickness of the external walls and balconies to the carpet area. Super built up area goes further, adding a share of common spaces such as the lobby, staircase, and lift areas. Because developers can decide how generously to calculate that common area share, super built up figures are not consistent from one project to the next, which is exactly why two flats can look similar on paper yet differ in real usable space.

The table below lays out how the measures compare, so you can see why the same flat can be described by very different numbers depending on which one a seller chooses to lead with.

Why does RERA make builders price on carpet area?

RERA makes builders price on carpet area to end the confusion that let flats look bigger than they were. Before the law, developers commonly quoted the super built up area, so a buyer paying for 1150 square feet might use only 800. By requiring that price and area be stated on the carpet basis, the law gives buyers a single, defined number they can compare across projects. It is now the developer's duty to make buyers aware of the carpet area and to quote on it rather than on an inflated super built up figure.

This does not stop a developer from also mentioning other numbers, and some still push saleable area figures that are not standardised. The protection is that the carpet area must be there, defined the same way for everyone, so you always have a fair basis to judge the deal.

What does this mean for a Mumbai buyer comparing flats?

It means you should compare flats on carpet area and treat every other number with caution. In a market like Mumbai, where per square foot rates are high, the difference between carpet and super built up can translate into a large sum. If one project quotes a rate on carpet area and another quotes a lower looking rate on super built up, the second can easily be the more expensive home once you convert both to the space you can actually use. Always ask for the rate per carpet area square foot, then compare like with like.

The same discipline helps with resale and rent later. Buyers and tenants increasingly speak in carpet area, so knowing your real usable size protects you at both ends. Our guide to what your agreement and sale deed should contain explains why the carpet area belongs in writing in those documents, not just in a brochure.

What is the loading factor, and why does it matter?

The loading factor is the gap between carpet area and super built up area, expressed as a percentage added on top of carpet. If a flat has a carpet area of 800 square feet and a super built up area of 1150 square feet, the extra 350 square feet is the loading, and here it is a little under half of the carpet area. A higher loading factor means you are paying for proportionately more wall and common space relative to your usable floor. Two flats with the same carpet area but different loading factors give you the same home, yet one may be quoted as far larger.

Because loading is not capped uniformly, it is a number worth asking about directly. A developer who is transparent about carpet area and loading is easier to trust than one who leads only with the biggest figure available.

A quick example shows why this matters in rupees. Suppose one Mumbai project quotes 25,000 rupees per square foot on a carpet area of 800 square feet, so the flat costs 2 crore for the space you can actually use. A second project quotes a lower looking 18,000 rupees per square foot, but on a super built up area of 1150 square feet, which works out to about 2.07 crore for a similar 800 square feet of real floor. The headline rate on the second looks cheaper, yet the home costs more once you measure both against usable space. Converting every quote to a carpet area rate is the only reliable way to see through that gap.

How do you verify the carpet area of your flat?

You verify it by checking the project's RERA registration record and the agreement, not just the brochure. Registered projects file their details with the state RERA authority, and the carpet area of each unit type is part of the record a buyer can inspect. Cross checking the brochure against the RERA page and against the figure written into your agreement is the surest way to confirm the number is genuine. Our explainer on how a project's RERA status affects buyers shows why that registration record is worth opening before you commit.

If the figures do not match across those three places, that is a question to raise before signing, not after. A clean, consistent carpet area is a small but telling sign of an orderly project.

What should you check before you book?

Run through these seven steps so you are always comparing the space you can actually use.

1. Ask for the RERA carpet area in writing, not only the built up or super built up figure.
2. Check that carpet area figure against the project's RERA registration page.
3. Confirm the price is quoted per carpet area square foot before you compare rates.
4. Read the agreement to see that the carpet area matches what you were shown.
5. Note that balconies and any private terrace are measured separately, not inside carpet area.
6. Compare competing flats on carpet area, since super built up figures are not standardised.
7. Raise any mismatch between brochure, RERA record, and agreement before you sign.

What is carpet area as defined by RERA?

Carpet area is the net usable floor area inside your apartment. Under Section 2(k) of the RERA Act 2016, it excludes external walls, service shafts, and exclusive balconies, verandahs, and open terraces, but includes the internal partition walls that divide your rooms. It is the floor space you can actually use, measured room to room within your flat.

Can a builder price a flat on super built up area?

No. Under RERA, developers must quote the price and area on the carpet area basis, not on super built up area. They may mention other figures, but the defined carpet area has to be disclosed and used for pricing, which gives buyers one consistent number to compare fairly across different projects.

Why is carpet area smaller than the size in the brochure?

Because older brochures often used super built up area, which adds external walls, balconies, and a share of common spaces like the lobby and lift on top of your usable floor. Carpet area strips those out to show only the space inside your flat, so it is naturally smaller but far more honest about what you get.

How do I confirm the carpet area is genuine?

Check it in three places and make sure they agree. Compare the carpet area in the brochure with the figure filed on the project's RERA registration page and the number written into your agreement. If all three match, the figure is reliable. If they differ, raise it with the developer and get it corrected before you sign.

Last updated 2026-07-20. PropNewz Team.