The carpet area is the space inside your flat that you can actually use, measured wall to wall. The built-up area adds the thickness of the external walls and your balcony. A super built-up area adds your share of lifts, lobbies, staircases and other common spaces. Under RERA, builders must disclose the carpet area, so that is the figure to compare.
Quick overview
• What it is: three ways of measuring the same flat, from smallest to largest.
• Where it is used: sale agreements, brochures, price quotes and property tax.
• Why it matters: knowing which area a figure refers to helps you compare flats on the same basis.
What is the carpet area under RERA?
Section 2(k) of the Real Estate (Regulation and Development) Act, 2016 defines carpet area as “the net usable floor area of an apartment, excluding the area covered by the external walls, areas under services shafts, exclusive balcony or verandah area and exclusive open terrace area, but includes the area covered by the internal partition walls of the apartment.”
In plain terms, it is the floor you can walk on and furnish, plus the strip under the walls between rooms. Since RERA, flats are sold on carpet areas, and it must be stated in the agreement for sale.
What is the built-up area?
Built-up area is the carpet area plus the external walls and your exclusive balcony or verandah. It is often 10% to 20% larger than the carpet area, and more if the balcony is large.
The RERA Act does not define built-up area, so builders may calculate it differently. Tamil Nadu property tax is generally assessed on plinth area, which is close to built-up area.
What is a super built-up area?
Super built-up area is the built-up area plus your share of common spaces such as lobbies, corridors, staircases, lift shafts, the clubhouse and gym. The extra area added for these shared spaces is called loading.
Loading of 25% to 40% over carpet area is common, and it tends to be higher in projects with more amenities. Brochures often show it alongside the carpet area, and your agreement for sale will state the carpet area as well.
How do carpet area, built-up area and super built-up area compare?
| Carpet area | Built-up area | Super built-up area | |
| Includes | Usable floor and internal walls | Carpet area, external walls, balcony | Built-up area and share of common spaces |
| Example (same flat) | 1,000 sq ft | 1,150 sq ft | 1,400 sq ft |
| Legal definition | Yes, RERA Section 2(k) | No | No |
| Where you see it | RERA registration, sale agreement | Plans, tax papers | Brochures |
| Fully usable indoors? | Yes | Mostly | No |
How do you compare flats across projects on the same basis?
Projects may present areas in different ways, so the simplest approach is to compare every flat on the same measure. Ask each builder for the carpet area, which RERA requires them to disclose, and look at the total cost against that figure.
Loading also varies from project to project, depending on the shared spaces each one offers. For example, two flats with the same super built-up area of 1,400 sq ft could have carpet areas of about 1,000 sq ft and 1,077 sq ft, if their loading is 40% and 30% respectively. Neither is better by default, because a project with a clubhouse, gym and landscaped grounds will naturally carry more common area. Knowing the carpet area simply shows you how much of the space is for your exclusive use and how much is shared.
Does carpet area affect GST?
Yes. The 1% affordable housing rate applies only when the carpet area is up to 90 sq m (about 969 sq ft) outside metros and the price is up to ₹45 lakh. Our guide to GST on residential property explains the rates.
What is UDS and why does it matter in Tamil Nadu?
UDS, or undivided share of land, is your share of the land the apartment building stands on. You own it jointly with every other flat owner.
Tamil Nadu buyers used to register a sale deed for the UDS and a separate construction agreement for the flat. Since 1 December 2023, new flats are registered through a single composite sale deed that covers both. The UDS is still stated in the deed, so check the figure.
UDS matters because the building will age but the land will not. If it is redeveloped decades from now, each owner’s share of the new building is based on their UDS.
How is UDS calculated?
Most builders use this formula: UDS = (super built-up area of your flat ÷ total super built-up area of all flats) × total land area.
Say a building stands on 20,000 sq ft of land and has 40 flats of 1,400 sq ft super built-up area each, or 56,000 sq ft in total. Your UDS is 1,400 ÷ 56,000 × 20,000, which comes to 500 sq ft.
More flats on the same land means a smaller UDS for each owner.
Does a higher floor get more UDS?
No. UDS is usually shared in proportion to the size of the flat, so a bigger flat gets more. The floor it is on makes no difference.
What should you check before you sign?
• The carpet area in the agreement for sale matches the carpet area shown on the project’s registration with TNRERA.
• The price per square foot, worked out on carpet area.
• The loading percentage, in writing.
• Balcony and terrace areas listed separately from the carpet area.
• The UDS in square feet, and the method used to calculate it.
For an under-construction project such as Windchimes Apartments in Ranipet, ask for these figures for the specific flat.
Key takeaways
Carpet area is the only one of the three with a legal definition, and it is the figure your price should be based on. In Tamil Nadu, check your UDS as well, because it is your share of the land.
Frequently asked questions
1. Does the carpet area include the balcony?
No. Under the RERA definition, the exclusive balcony, verandah and open terrace attached to a flat are excluded from the carpet area. The builder can still charge for them, but they should be shown as separate figures in the agreement for sale, so ask for each area in writing.
2. How much bigger is the super built-up area than the carpet area?
In most apartment projects, the super built-up area is 25% to 40% larger than the carpet area. The difference, called loading, depends on how many shared spaces the project has, such as lifts, lobbies, a clubhouse or a gym. More amenities usually means higher loading.
3.How do I convert square metres to square feet?
Multiply by 10.764. One square metre equals 10.764 square feet, so a carpet area of 90 sq m is about 969 sq ft. GST rules often use square metres, while builders in Tamil Nadu usually quote square feet, so convert before you compare.
4. Is UDS the same as plot area?
No. A plot area is land you own outright, with its own boundaries. UDS is an undivided share of the land under an apartment building, held jointly with the other flat owners. You cannot fence it or sell it separately from your flat, and it is recorded in square feet in your sale deed.
This article is general information, not legal or tax advice. Rules on registration and GST can change, so confirm the details with a lawyer or chartered accountant before you sign.
