Cent, ground and square feet: the Tamil Nadu land units, converted

The conversions

These are fixed definitions, not local variations. A cent is one-hundredth of an acre, and a ground is a Chennai-area unit that settled at 2,400 square feet.

Why a ground is 2,400 square feet

The ground is a survivor of the Madras Presidency measurement system, where it described a plot roughly 40 by 60 feet — a standard residential frontage of the period. The 2,400 figure is that rectangle, and it stuck even though plots stopped being that shape.

This matters because a ground is not a round number in any other system. It is 5.5102 cents and 222.97 square metres, both awkward. Anyone converting by memory tends to round a ground to 5.5 cents, which under-measures by about 0.2% — negligible on one plot, visible on a layout of forty.

Where the units collide on a real project

A builder in Tamil Nadu routinely handles three units on the same project, and each is attached to a different document.

• The land is bought and sold in cents or grounds, and that is what the sale deed says.
• The construction is quoted to the client in rupees per square foot of built-up area — a different quantity from the land area entirely.
• The plan submitted to CMDA or DTCP is in square metres, because the development control rules are written that way.
• FSI and coverage limits are ratios against the plot area, so an error in the plot conversion propagates into the permissible built-up area.

The mistake that actually costs money

The expensive error is not arithmetic. It is quoting a per-square-foot rate against the wrong area.

A 2,400 sq ft plot — one ground — with a two-floor house on 60% coverage has roughly 2,880 sq ft of built-up area. A rate quoted per square foot of plot rather than per square foot of built-up area understates the job by about 20%. The arithmetic is trivial; the ambiguity in the sentence "₹2,000 a square foot" is what causes the loss.

The fix is a quotation that states the area, the unit and what the area refers to, on the same line as the rate. Not "2,400 sq ft at ₹2,000" but "built-up area 2,880 sq ft at ₹2,000 per sq ft of built-up area".

A note on "square feet" itself

Built-up area, carpet area and super built-up area are three different numbers for the same house, and only carpet area has a statutory definition — RERA defines it as the net usable floor area within the walls. Super built-up area has no legal definition at all, which is precisely why it is the one used in advertising.

For a construction contract, say which one the rate applies to. For anything sold to a buyer under RERA, carpet area is the one that has to be disclosed.