Carpet area vs built-up area: one Navi Mumbai flat, three rates

Which of two flats gives you more home for the money? You’d think the price sheets would say. But one sheet says carpet area (the floor inside your walls that you can walk on). The next says built-up, and a portal says super built-up.

So the price of each square foot jumps around. Is a flat cheap, or just measured bigger? The quiet worry: are you paying for floor you’ll never stand on?

Maybe you rent in Kharghar. You’re weighing a 2 BHK there against a bigger one in Panvel or Taloja. I won’t tell you which to buy. I’ll show you the one size the law defines. Then we’ll run real flats through the sum.

The short answer: compare flats on carpet area and on the total cheque. A rate that doesn’t say “carpet” can’t be compared with one that does.

Only carpet area is defined by law; the other two are trade terms

RERA (the 2016 central law for new homes) defines only one of the three sizes. That’s carpet area. Built-up and super built-up don’t appear in it.

Here are the words of section 2(k) of the Act. Carpet area is “the net usable floor area of an apartment”. It leaves out the outer walls and service shafts. It also leaves out your own balcony and open terrace.

Size	What it counts	Who sets it
Carpet area	The floor inside your walls, plus the walls between rooms	The law, section 2(k)
Built-up area	Carpet area plus the outer walls, and often the balcony	No law; each builder
Super built-up area	Built-up area plus a share of the lobby, lifts and stairs	No law; each builder

Think of a shared auto. Carpet area is your seat. Super built-up is your seat plus a share of the whole auto. You pay for all of it, but you only sit in one place.

One flat can show three different rates for the same cheque

Take the 2 BHK at Mass Insignia in Kharghar. It has 576 sq ft of carpet area.

Its page lists it from ₹81.57 lakh. That’s the cheque, whichever size you divide it by.

Divide it by the carpet area and you get ₹14,161 for each sq ft. That’s the honest rate, because it’s the floor you’ll live on.

Carpet, 576 sq ft₹14,161

Built-up, assumed 10% over carpet₹12,874

Super built-up, assumed 43% over carpet₹9,903

The two bigger sizes are my guesses, not this builder’s figures. Builders set their own. For built-up I used 10% more than carpet. That’s the lower of two government multipliers, explained below.

For super built-up I used 43%. That’s the average gap Anarock, a property research firm, found in the Mumbai region in early 2025. The report doesn’t say if it measured on carpet or on total area. So treat that row as a rough picture.

The bottom row looks over ₹4,000 cheaper for each foot. Yet not one rupee of the price moved.

Compare two flats on carpet area and the total cheque

So use just two numbers: the carpet area and what you’ll pay in total. Here are three real 2 BHKs, each divided by its carpet area.

2 BHK	Carpet area	Starting price	₹ for each carpet sq ft
Mass Insignia, Kharghar	576 sq ft	₹81.57 lakh	₹14,161
Alankara Paradise, Panvel	665 sq ft	₹74.75 lakh	₹11,241
Arihant Anaika, Taloja	663 sq ft	₹49.25 lakh	₹7,428

The Panvel 2 BHK has 89 more square feet, and it starts lower.

That doesn’t make it the better home for you. Part of Kharghar’s higher rate may be its location. Only you can weigh that against your commute.

The keys come at different times, too. The Kharghar flat’s registered handover month is December 2027.

The other two show December 2026. So ask each builder where the occupancy certificate (the letter saying the building is fit to live in) stands. And count the rent you’d still pay.

These are starting prices. GST (the tax on a flat still being built) comes on top. So do stamp duty (the state’s tax on a property sale) and registration. Compare totals with the same extras.

The simple rule: compare flats on the carpet area written in the agreement and on the total cheque. If a rate doesn’t say “carpet”, ask for the carpet area and work the rate out yourself.

Carpet area is the part you live in every day

What’s 89 square feet at home? Roughly a room 9 feet by 10. That’s a small bedroom, or space for a cupboard and a study table.

It also sets a monthly bill. In the state’s model agreement, your share of running costs goes by carpet area. Think water charges and the watchman’s salary, until the society takes over.

And think about the monsoon. An open balcony is where the washing dries, and in a wet week it won’t. So check each flat’s balcony as closely as its rooms.

Loading is the gap, and Anarock says no law limits it

Loading is the extra area added on top of your carpet area. It pays for the lobby, lifts and stairs you share.

Anarock’s early-2025 figure for the Mumbai region is the one in the chart above. As its Prashant Thakur put it, “no law currently limits the loading factor”.

If a sheet shows a loading figure, ask: a share of what? Some measure it on carpet area and some on the total. One report even uses both.

So don’t argue about loading. Ask for the carpet area. Every new project must register with MahaRERA (Maharashtra’s regulator for new homes). When it does, the law makes the builder file the carpet area of each flat type. Balconies and open terraces are listed on their own.

Your own balcony isn’t carpet area, but it must be listed

An open balcony that’s only yours sits outside carpet area. The Act calls it the “exclusive balcony or verandah area”. That means one attached to your flat, for you alone.

So a big balcony can mean a smaller carpet area. You haven’t lost it. It’s on its own line.

What about a balcony closed in with walls or glass? I couldn’t find a MahaRERA order that settles it, so I won’t guess. Ask the builder to put in writing whether it’s counted.

Selling an older flat to move up? L&T Realty’s note says the older flat law, MOFA, counted the balcony inside carpet area. So your old carpet area and a new one may not match.

The agreement fixes the carpet area, and the price follows it

The agreement for sale (the contract you sign and register with the builder) fixes the size you pay for. Any carpet area on a website, ours too, is the builder’s figure until then.

A builder can’t take more than 10% of the price before that agreement is registered.

The state’s model agreement is Annexure A (an attachment at the end) of Maharashtra’s 2017 RERA rules, on MahaRERA’s site. Its clause 1(g) caps the change in carpet area at 3%. The price follows the area. Find the same clause in your own draft.

1. Booking You pay no more than 10% before the agreement is registered.
2. Agreement It states your carpet area in square metres. Ask for the balcony and terrace on their own lines.
3. Building finished The occupancy certificate arrives. The builder then confirms the final carpet area.
4. Came out smaller Within the 3% cap, you get the extra back within 45 days, with interest.
5. Came out bigger The builder asks for more at your next payment, at the same rate.

What’s that cap on a real flat? On the Mass Insignia 2 BHK, 3% is about 17 sq ft.

At that flat’s rate, that’s roughly ₹2.4 lakh. So check the final figure in the builder’s letter.

Stamp duty is worked on built-up area, through the government’s value

Stamp duty is charged on the higher of two figures. One is your agreement price. The other is the ready reckoner value (the government’s own rate card for each area).

That rate card uses built-up area, not carpet. It gets there by multiplying your carpet area by a fixed number.

A 2015 article gives that number as 1.2. A 2026 summary gives 1.1 for newer flats outside Mumbai. I can’t tell you which your building gets.

So ask your advisor, or the sub-registrar’s office (the government office where your agreement gets registered). You can also look the value up on the state registration portal. Our stamp duty guide for Navi Mumbai works out the full bill.

Rates per foot still help for a rough feel, not for choosing

Use rates per foot for a rough feel for an area, as in our guide to Kharghar flat prices. Don’t pick between two flats on them unless you know which size was used.

Everyone talks in rates per foot, so is this just theory? Not once you see who it matters for.

• First-home couples: the carpet area decides if the second bedroom fits a bed and a cupboard.
• Investors: tenants pay for usable floor, so work returns on carpet area.
• Families moving up: compare your old carpet area with the new one like for like.

What I’d check before you pay a token

• The carpet area for your flat type, in the builder’s filing on MahaRERA’s site and in the draft agreement. They should match.
• The balcony and terrace, each on its own line.
• An enclosed balcony: in or out of the carpet area, in writing.
• The total cheque: price, GST, stamp duty, registration, parking and society charges.

Not sure the project is registered at all? Start with how to check a MahaRERA registration yourself.

Send us the two or three flats you’re weighing. We’ll put each one’s carpet area and total cheque side by side. The form is on our pages for Kharghar, Panvel and Taloja. Let’s make sure the floor you pay for is the floor you get.

How we checked: sizes, prices and handover months are from each project’s 10Projects page, read 2 November 2026. Each rate is price divided by carpet area. Check your own flat the same way.

Questions buyers ask

Can a builder still talk in super built-up area?

Brochures sometimes do. But the state’s rules make a builder tell MahaRERA each flat’s carpet area, even if it was sold on super built-up.

My agreement gives square metres. How do I convert?

One square metre is about 10.76 square feet.

What if the area changes by more than the cap?

The model clause covers changes up to 3%. It doesn’t say what happens beyond that. So ask a lawyer or MahaRERA before you sign.

Buying your first home here? Our six steps to buying a flat in Navi Mumbai put this in order, from the loan to the keys.