How Big Is Your New Flat Really? RERA Carpet to Built-Up Math

Builders quote built-up and super built-up because the numbers look larger. Here is the plain arithmetic that converts any quoted figure back to RERA carpet area — and the one mistake almost everyone makes doing it.

Built-up area is typically carpet plus 10-20%; super built-up is carpet plus 25-40%. To work backwards, divide rather than subtract: 700 sq ft super built-up at 30% loading is 700/1.30 = 538 sq ft carpet. Loading percentages are market practice, not law.

Redevelopment offers are quoted in whatever number sounds biggest. The arithmetic below turns any of those numbers back into the one that matters — carpet area.

What is the actual sum from carpet to built-up?

Start from carpet: under the Real Estate (Regulation and Development) Act 2016, carpet area is the net usable floor area of the flat, excluding external walls, service shafts, exclusive balcony or verandah and exclusive open terrace, but including internal partition walls. DCPR 2034 uses the same meaning.

Built-up area adds wall thickness and features such as balconies — commonly 10-20% more than carpet. Super built-up, or "saleable", area additionally loads a share of lobbies, staircases, lifts and passages — commonly 25-40% more.

Carpet 500 sq ft, 15% loading: built-up = 500 x 1.15 = 575 sq ft.
Carpet 500 sq ft, 30% loading: super built-up = 500 x 1.30 = 650 sq ft.
Working in metric? 46.45 sq m x 10.7639 = 500 sq ft.

Why does subtracting the loading give the wrong answer?

This is the most common error we see in society meetings. Given 700 sq ft super built-up at 40% loading, people subtract 40% and get 420 sq ft. Wrong. You must divide: 700 / 1.40 = 500 sq ft carpet. Subtracting understates your flat by 80 sq ft here — and in a 100-flat society, that is a very large misunderstanding of the project. Run your own figures through our carpet to built-up converter, and check any promised increase with the additional area calculator.

So which number should the agreement carry?

Only carpet. Those 10-20% and 25-40% ranges are typical market practice, not statute — there is no legally fixed loading percentage, and different builders compute them differently. What the law does settle is that every sale agreement must state the flat in carpet area. Insist on the carpet figure in writing, in sq ft and sq m, before signing anything. Our FAQ and glossary explains the surrounding terms, and a chartered accountant or advocate should review the final documents.

Work it out for your own society

Enter any figure a builder has quoted you — carpet, built-up or super built-up, in sq ft or sq m — and see the other numbers instantly, with the loading percentage shown openly so you know exactly what you are being sold.

Open the Carpet to Built-Up Converter

Common questions

How do I convert super built-up area back to carpet area?

Divide, do not subtract. If a flat is quoted at 650 sq ft super built-up with 30% loading, carpet is 650 / 1.30 = 500 sq ft. Subtracting 30% would wrongly give 455 sq ft.

Is there a legal limit on loading percentage in Mumbai?

No. The 10-20% built-up and 25-40% super built-up ranges are typical market practice, not statute. There is no statutory loading percentage. What the law does require is that every sale agreement states the flat in carpet area.

How do I convert square metres to square feet?

Multiply by 10.7639. So 46.45 sq m equals 500 sq ft. Ask for both units in writing, because offer letters often switch between them.