The components
| Included in built-up area | Not included |
|---|---|
| Carpet area of every room | Lift lobbies and corridors |
| Internal partition wall thickness | Staircases and fire escapes |
| External wall thickness | Society office, gym, clubhouse |
| Balcony and terrace area | Parking, generator and pump rooms |
| Utility and dry balcony | Shafts serving the whole building |
A worked example
Take a Mumbai 2BHK with a carpet area of 620 sq ft. The internal partitions and external walls account for roughly 55 sq ft of footprint, and a 6 ft × 4 ft balcony adds 24 sq ft. Built-up area is therefore about 700 sq ft — a 13% uplift. Apply the developer's loading factor of, say, 30% on top and the super built-up figure becomes 910 sq ft, which is the number the flat was advertised at.
Where the figure is actually used
- Property tax assessment in several municipalities, including parts of Maharashtra.
- Construction cost estimation by developers, who build walls and balconies and must pay for them.
- Approval drawings and FSI calculations, in the form of the built-up area the plan sanctions.
- Older sale agreements, pre-RERA, which frequently quoted built-up rather than carpet.
One thing changes the figure after possession: enclosing a balcony. It converts balcony area into internal area, which alters the built-up figure, and in most Mumbai societies it needs permission and may breach the sanctioned plan. It is common, it is frequently unauthorised, and it complicates a later sale.
Why interiors are not quoted on it
Because you cannot furnish a wall. An interior rate applied to built-up area includes 80 sq ft of masonry in a 700 sq ft figure, which inflates the apparent scope and deflates the apparent rate. When a quotation uses built-up area, ask for the same total restated against carpet area — the number will be the same and the rate will be 10–15% higher, which is the honest figure. See the area converter and the full explanation.
Frequently asked questions
How much more is built-up than carpet area?+
Typically 10–15%. Thicker external walls, more internal partitions and a larger balcony push it towards the upper end. A studio with few internal walls sits nearer 8%.
Is built-up area used in RERA agreements?+
No. RERA requires the carpet area to be stated, precisely because built-up and super built-up were being used inconsistently before 2016. Older agreements may still quote built-up area.
Does built-up area include the balcony?+
Yes. Balconies, terraces and dry balconies form part of built-up area, which is one of the main reasons it exceeds carpet area. They are excluded from carpet area entirely.
Which area is used for property tax?+
It varies by municipality. In much of Maharashtra, property tax is assessed on carpet area under the capital-value system, though built-up area appears in several other states' assessments. Check your own tax bill.