Carpet area vs built-up vs super built-up: what RERA says and what you actually get
Builders quote super built-up area, you live in carpet area, and the gap is often 25–40%. The legal definitions, typical loading factors, and how to compare two flats fairly.
3 min read · Published 2026-10-31 · Last reviewed 2026-10-31
Two flats are advertised at ₹8,000 per square foot. One is 1,000 sq ft super built-up, the other 1,000 sq ft carpet. The second is roughly 40% bigger inside. Until 2017 nothing stopped a builder from quoting whichever number flattered the price. The Real Estate (Regulation and Development) Act changed that, but the older numbers still appear in brochures, resale listings and bank valuations, so you need to know all three.
The three areas
Carpet area is the net usable floor area of the apartment: every room, the kitchen, bathrooms and internal passages, measured wall to wall. RERA's definition includes the area covered by internal partition walls and excludes external walls, service shafts, balconies, verandas and open terraces. This is the number you can lay carpet on, plus the internal walls.
Built-up area adds the thickness of external walls and the balconies and verandas attached to the flat. It is usually 10–20% more than carpet area, depending on wall thickness and how many balconies there are. RERA does not define built-up area; it is a trade term.
Super built-up area adds your proportionate share of common areas: lobby, staircases, lift shafts, corridors, clubhouse, gym, security room and sometimes the swimming pool deck. The addition is called the loading factor and runs anywhere from 20% to 50% of carpet area. Super built-up area is a pricing convention, not a measurement of anything you own exclusively.
What RERA requires
Under RERA, a promoter must disclose and sell on carpet area, and the agreement for sale must state the carpet area. If the final carpet area is smaller than promised, the builder refunds the difference at the agreed rate; if it is larger, the buyer pays for the excess up to a 3% cap. Builders may still mention super built-up area, but the carpet area must be stated and the price per square foot of carpet area is what you should compare.
The protection applies to projects registered with the state RERA authority. Resale flats and projects completed before RERA are outside it, so expect older listings to quote super built-up.
Typical loading factors
| Project type | Carpet to super built-up loading |
|---|---|
| Older standalone buildings, few amenities | 15–25% |
| Mid-range society with lift, lobby, parking | 25–35% |
| Premium towers with clubhouse, pool, large lobbies | 35–50% |
A 40% loading means a 1,000 sq ft carpet flat is sold as 1,400 sq ft super built-up. At the same quoted rate it costs 40% more than a flat sold on carpet area.
Converting between them
The engine behind our calculator uses two factors you can set:
- Built-up = Carpet × (1 + wall and balcony loading). Default 15%.
- Super built-up = Built-up × (1 + common area loading). Default 25%.
So a 1,000 sq ft super built-up flat with those defaults has 800 sq ft built-up and about 696 sq ft carpet. The real price per carpet square foot is the quoted rate multiplied by super built-up and divided by carpet: ₹8,000 quoted becomes ₹11,500 per carpet square foot.
How to compare two flats fairly
- Get the RERA carpet area of each from the registered agreement or the state RERA website, where every registered project lists unit-wise carpet areas.
- Divide the all-in price (price plus GST and other charges) by carpet area.
- Compare those numbers, then judge the amenities separately. A higher loading is not bad if you will use the clubhouse; it is bad if you are paying for a lobby you walk through twice a day.
Where the numbers matter later
- Stamp duty is charged on the agreement value, which is usually computed on super built-up or the ready reckoner rate per square metre of built-up area, depending on the state.
- Property tax in most municipalities uses built-up or carpet area.
- Resale buyers increasingly ask for carpet area, so a flat with a 45% loading is harder to sell at the same per-square-foot rate as one with 25%.
- Interior budgets should use carpet area; nobody tiles the lift shaft.
Convert any figure and see the true per-square-foot price with the carpet vs built-up calculator, and carry the result into the property purchase cost calculator.
Sources
This guide is general information, not financial, tax or legal advice. Rules change; the review date above tells you when it was last checked. See our editorial policy.