Carpet area vs built up area vs super built up area: what you are really paying for

A Kolkata developer quotes you a 957 sq ft 2 BHK. You walk in with a tape and measure about 628 sq ft of floor you can actually use. Nobody lied to you. They just used a different number.

That gap is the difference between carpet area, built up area and super built up area. If you compare flats without knowing which one you are looking at, you will overpay. Here is how to read all three.

What carpet area means under RERA

Carpet area is the space inside your flat that you can actually use. RERA defines it in Section 2(k) as the net usable floor area of an apartment, excluding the area covered by external walls, service shafts, exclusive balconies or verandahs and exclusive open terraces, but including the internal partition walls.

In plain terms: measure every room wall to wall, add the kitchen and toilets, and you have roughly the usable area. Since RERA, developers have to state the usable area in the agreement for sale, and West Bengal projects registered with WBRERA follow the same rule.

The carpet area is the only number that tells you how much home you are getting. Everything else adds things you share, or things you cannot put furniture on.

Built up area: usable floor plus walls and balcony

Built up area is the usable area plus the thickness of the external walls, plus your exclusive balcony or terrace. It is the footprint of your flat as a block on the floor plan.

In most Kolkata buildings, the built up area runs about 10% to 20% above the usable area, depending on wall thickness and balcony size. A flat with a big balcony shows a bigger gap. That balcony is real space, but you cannot put a bed on it, so do not count it as a room.

Super built up area: where the loading sits

Super built up area (SBUA) is the built up area plus your proportionate share of every common area in the building: lobby, staircase, lift wells, corridors, the clubhouse, the generator room and sometimes the security cabin. This share is called loading.

Developers in Kolkata still advertise in SBUA because the number is bigger and the per sq ft rate looks smaller. A loading of 25% to 35% over built up area is common in normal buildings. Projects with a large clubhouse, pool and amenity floors often go higher.

Loading is not a scam on its own. You do get to use the lobby and the pool. The problem is when two flats with very different loading are compared on the SBUA rate as if they were the same thing.

Carpet area vs built up area in real Kolkata flats

Here are three real flats we sell, with the developer's own figures:

• Martin Burn Rupsha, Behala, 2 BHK: 957 sq ft SBUA, 628 sq ft carpet area. The super built up figure is about 52% above the usable area.
• Sunshine 2, Uttarpara, 2 BHK: 630 sq ft SBUA, 400.4 sq ft usable area plus a 10.8 sq ft balcony. About 57% above carpet.
• Sunshine 2, Uttarpara, 3 BHK: 840 sq ft SBUA, 571.4 sq ft usable area plus a 17.7 sq ft balcony. About 47% above carpet.

Notice the 3 BHK in the same project has a lower loading than the 2 BHK. Bigger flats often carry proportionally less common area. That alone can change which unit is better value.

A quick rule: in a normal Kolkata apartment, expect the usable area to be roughly 65% to 75% of the SBUA. If it is well below that, ask why.

How to compare flat prices on carpet area

Always convert the price to a rate per sq ft of usable area before you compare two projects.

Martin Burn Rupsha's 2 BHK at about ₹84 L works out to roughly ₹8,800 per sq ft on SBUA, but about ₹13,400 per sq ft of usable area. Sunshine 2's 2 BHK at about ₹33.76 L is roughly ₹5,360 per sq ft on SBUA and about ₹8,430 per sq ft of usable area.

The rate on usable area is the honest comparison. A project that looks cheaper per super built up sq ft can easily turn out to be more expensive per usable sq ft once you strip out the loading.

Two more checks:

• Ask whether the quoted usable area includes the balcony. Under RERA it should not, but brochures are not always careful.
• Check the usable area in the agreement for sale against the brochure. The agreement is what you can enforce.

Which area your costs are based on

The area used changes more than the price of the flat:

• Maintenance: most Kolkata buildings charge maintenance per sq ft of SBUA, so high loading costs you every month.
• Property tax: the municipality assesses on its own measured covered area, not on the brochure. See our guide to property tax in Kolkata.
• Stamp duty: it is calculated on the higher of the agreement value and the government's market value, not directly on area. Our stamp duty guide explains how.
• Home loan: banks lend against the property value, but their valuer will measure the flat. A big gap between the brochure and the valuation can reduce your loan.

What to ask before you book

Before you pay a booking amount on any flat, get these four numbers in writing: usable area, balcony area, built up area and SBUA. Then ask what the common areas are and how they were divided between flats.

If a sales team will only give you the SBUA, that is a sign to slow down. Every RERA-registered project has the usable area on its registration. You can check it yourself using our guide to verifying RERA registration.

Send us any brochure and we will do the maths

Share the brochure or price sheet for any Kolkata project and we will give you the usable area, the loading and the real price per usable sq ft, so you can compare flats on the same basis.

See our rentals service, browse verified properties, or talk to our legal and loan help desk. We are a RERA-registered agent, WBRERA/A/HOW/2025/000651. This is general guidance and not legal advice; check the specifics for your property with a professional.