When a builder says your flat is "1000 sqft", what they don't say is that you might only get 670 of those as actual usable space. The rest is wall thickness, balconies, lobbies, and the swimming pool you'll use twice a year. Here's how to read every property listing properly.
The three definitions, simply
1. Carpet area — what you can actually walk on
Carpet area is the usable floor space inside your apartment, measured wall-to-wall on the inside. Imagine you could literally roll out a carpet — that's carpet area. It excludes the thickness of walls, balconies, lobbies, and any common areas.
This is the area you'll furnish, live in, and pay maintenance on. RERA defines this as the official measurable area for sale.
2. Built-up area — adds wall thickness and balconies
Built-up area = carpet area + the thickness of internal walls + balcony area + utility/service ducts that fall within your unit boundary. It's typically 10–15% more than carpet area.
Built-up is sometimes called "plinth area" in older documentation. It represents the actual physical footprint of your apartment when you draw a line around the entire outside of your walls.
3. Super built-up area — adds your share of common areas
Super built-up area = built-up area + your proportionate share of common areas in the building — lobbies, staircases, lift wells, club house, swimming pool, gym, security cabin, gardens. The additional percentage added on top of built-up area is called the loading factor.
Loading factor varies enormously between projects: a basic walk-up apartment may have 18–22% loading; a luxury project with extensive amenities might charge 40–50% loading.
A worked example: 2BHK in Pune
You're looking at a 2BHK in Hinjewadi. The builder's brochure says: "1,050 sqft, ₹6,500/sqft, ₹68.25 lakh." Sounds reasonable. Let's break it down properly.
Now do the same exercise for the other 2BHKs you're shortlisting. The "₹6,500/sqft" project might actually be more expensive per usable sqft than the "₹6,800/sqft" project next door if the latter has a 22% loading factor instead of 32%.
What loading factors are reasonable in 2026?
| Project type | Typical loading | What's included |
|---|---|---|
| Standalone walk-up (3–4 storey) | 18–22% | Staircase, common entry. No lift. |
| Mid-range gated society | 25–32% | Lift, basic clubhouse, security, parking. |
| Premium gated community | 32–40% | Multiple lifts, large clubhouse, swimming pool, gym, gardens. |
| Luxury / large township | 40–50% | Multiple amenity blocks, indoor sports, party hall, sometimes commercial floors. |
| "Super luxury" | 50–60% | Concierge floors, spa, helipad. Verify all amenities exist before signing. |
Anything above 45% needs verification — ask the builder for the carpet-to-super-built-up ratio in writing, and verify against the RERA-registered project document at your state's RERA portal.
The RERA rule (and why builders sometimes ignore it)
The Real Estate (Regulation and Development) Act, 2016 mandates that:
- Every sale agreement must state the carpet area.
- The price quoted in the agreement must be on a per-carpet-sqft basis.
- Marketing materials may use super built-up terms, but the legal sale and registration must be on carpet area.
In practice: many builders still write up sale agreements quoting super built-up area, and most buyers don't push back. The agreement is technically still valid (because the carpet area is mentioned somewhere in the annexure), but the per-sqft headline is misleading.
How to convert quickly in your head
Standard conversion factors most projects use:
- Built-up = Carpet × 1.12 to 1.15 (i.e., add 12–15% to carpet for built-up)
- Super built-up = Carpet × 1.30 to 1.45 (i.e., add 30–45% to carpet for super built-up)
- Going the other way: Carpet ≈ Super built-up × 0.70 to 0.77
The single most useful number to memorise: a typical Indian apartment's carpet is roughly 70–75% of super built-up area. If a builder claims 1,000 sqft super built-up, your carpet is probably 700–750 sqft. Use this for instant sanity checks at site visits.
The home loan implication
Banks lend based on the property value (which is super built-up × rate per super built-up sqft, in practice — even though RERA says agreements should be on carpet). Your loan eligibility doesn't change based on how the area is quoted, but two things do:
- Stamp duty is calculated on the agreement value (the total amount), not on a particular area definition. So this doesn't change either.
- Property tax is calculated on built-up area in most municipalities (BMC Mumbai, BBMP Bangalore use built-up; some smaller cities use carpet). Confirm with your local municipal corporation.
Why this matters when comparing projects
Two real listings on the same day in the same Bangalore micromarket (Whitefield, May 2026):
| Project | Quoted | Loading | Real ₹/carpet sqft |
|---|---|---|---|
| Project A | ₹7,200/sqft (super built-up) | 43% | ₹10,296 |
| Project B | ₹7,800/sqft (super built-up) | 26% | ₹9,828 |
Project A looks cheaper at first glance — it isn't. Project B is actually 4.5% cheaper per usable sqft. This kind of comparison only works when you've forced both numbers to the same base. Always compare on carpet rate.