Derives permissible FSI from your plot, road width, and building height under TNCDBR 2019. Calculates premium FSI charges and Metro corridor discount automatically.
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Plot area | — |
Building tier | — |
Permissible FSI Derived from road width × high-rise threshold (18.30m) | — |
Max built-up area (base) plot × FSI | — |
Premium FSI tier By road width: 9–12m → 30%, 12–18m → 40%, 18m+ → 50% | — |
Additional area via premium FSI | — |
Premium charge factor Non-HR pays 50% of GV; HR pays 40% of GV — fixed by building type, not road width | — |
Premium FSI charge (base) | — |
Metro / MRTS 500m discount 50% off premium charge if within 500m of MRTS / suburban / Metro corridor | — |
Net premium charge | — |
Ground coverage cap | — |
Min floors required | — |
Estimated carpet area Built-up × 0.78 | — |
Permissible FSI by building tier and road width, per TNCDBR 2019 Sections 35 (non-high-rise) and 39 (high-rise).
| Building tier | Road width | FSI | Ground coverage |
|---|---|---|---|
| Non-high-rise (≤ 18.30m) | Any | 2.0 | ~60–65% (via setbacks) |
| High-rise (> 18.30m) | 12m | 2.0 | 50% max |
| High-rise (> 18.30m) | 15m | 2.5 | 50% max |
| High-rise (> 18.30m) | 18m+ | 3.25 | 50% max |
High-rise on roads narrower than 12m is not permitted. Premium FSI adds an extra 30% (9–12m road), 40% (12–18m road), or 50% (18m+ road) on top of base FSI; charge factor is 50% of GV for non-HR and 40% of GV for HR. Metro / MRTS 500m corridor halves the premium charge.
Common scenarios at GV ₹5,000/sqft. Numbers rounded.
| Plot | Road / Height | Permissible FSI | Max built-up |
|---|---|---|---|
| 2,400 sqft non-HR | 9m road / 12m height | 2.0 | 4,800 sqft |
| 4,000 sqft high-rise | 12m road / 30m height | 2.0 | 8,000 sqft |
| 4,000 sqft high-rise | 15m road / 30m height | 2.5 | 10,000 sqft |
| 4,000 sqft high-rise | 18m road / 30m height | 3.25 | 13,000 sqft |
| 4,000 sqft high-rise | 18m road + premium | 4.875 | 19,500 sqft |
| 4,000 sqft on 9m road | 40m height (high-rise) | — | Infeasible: road < 12m |
Premium FSI is opt-in and chargeable. Add the premium charge to project cost when modelling viability.
Floor Space Index — also called FAR (Floor Area Ratio) — is the ratio of total built-up area on a plot to the plot area itself. An FSI of 2.0 on a 2,400 sq ft plot allows 4,800 sq ft of total built-up area across all floors. FSI is set by the local planning authority and is the single most important number controlling how much you can build. It directly determines project economics, unit count, and saleable area.
Unlike calculators that ask you to type the FSI you think applies, this tool derives the permissible FSI from your inputs under TNCDBR 2019. The first switch is the high-rise threshold: any building taller than 18.30m is classified as high-rise (Section 39). At or below 18.30m, the building is non-high-rise (Section 35) and the FSI is a flat 2.0 across CBA, EWS, and Other Area zones. For high-rise buildings, FSI is set by the abutting road width: 12m road allows FSI 2.0, 15m allows 2.5, and 18m or wider allows 3.25 — the highest base FSI under the rules. If your road is narrower than 12m, high-rise construction is not permitted and the calculator flags this as infeasible.
Premium FSI lets you build above the base FSI by paying a charge to the planning authority. Two parameters drive the math, and they are commonly conflated. First, road width controls the percentage of additional FSI you can purchase: a 9–12m road allows 30% extra, 12–18m allows 40% extra, and 18m or wider allows 50% extra. Second, the charge percentage of guideline value depends on building type — not road width: non-high-rise buildings pay 50% of guideline value per unit of additional plinth area, while high-rise buildings pay 40%. Several public calculators (including verified.realestate) show the charge percentage varying by road width — that is incorrect and conflates the two axes. This calculator separates them correctly.
Per the 2022 amendment to TNCDBR, properties within 500m of MRTS, suburban (EMU), or Metro Rail corridor centerlines receive a 50% reduction on premium FSI charges. The net effective rate becomes 25% of guideline value for non-high-rise and 20% for high-rise. The corridor measurement is taken from the rail centerline; if your plot is partly inside and partly outside the 500m band, applicability is determined by the planning authority case by case. Confirm corridor classification (MRTS vs suburban vs Metro) and exact buffer with your local CMDA / DTCP office before relying on the discount.
Permissible FSI is the maximum total floor area you can build, but ground coverage rules cap how much of that floor area can sit on each individual floor. For high-rise buildings, ground coverage is capped at 50% of plot area regardless of FSI — a 2,400 sq ft plot at FSI 3.25 yields 7,800 sq ft of total built-up, but each floor cannot exceed 1,200 sq ft (50% × 2,400). The minimum floor count is therefore ceil(7,800 / 1,200) = 7 floors. This calculator surfaces the minimum floors required so you do not silently violate ground coverage. For non-high-rise, ground coverage is governed by setback rules rather than a hard cap; effective coverage typically lands at 60–65%. Front setbacks scale with road width (1.5m for roads under 9m, 3m for 9–18m, 4.5m for 18–30.5m, 6m for above 30.5m). Side and rear setbacks scale with building height.
Built-up area (BUA) is the total area enclosed by external walls including walls, balconies, and common areas. Carpet area is the usable floor area inside a unit, excluding external walls and common spaces — central RERA Section 2(k) is the authoritative definition and TNRERA follows it. The carpet-to-built-up ratio in Tamil Nadu residential projects is typically 0.75 to 0.80, so this calculator estimates carpet at 78% of built-up area. Super built-up (or saleable) area adds a proportionate share of common amenities and is typically 1.2 to 1.35 times the carpet area. RERA mandates carpet area disclosure on every sale; never confuse it with the built-up or super built-up figure.
TNCDBR Rule 29 excludes several spaces from the FSI calculation, effectively giving you free additional usable area. These include: terrace structures (staircase rooms, lift rooms, mumty, lift machine rooms, water tanks under 1.5m height, WCs under 10 sq m, architectural features); parking (all basement parking, open-sided stilt parking, staircase and lift cores serving parking); and service areas (servant quarters in non-high-rise residential, watchman and caretaker booths, sewage and water treatment plants, service ducts, and balconies up to 5% of unit area). Anything beyond these caps counts against your FSI quota. This calculator computes raw FSI; on a real project, the exclusions can add 10–25% additional usable area on top of the FSI output.
Inside the Chennai Metropolitan Area (1,189 sq km), the Chennai Metropolitan Development Authority (CMDA) administers TNCDBR 2019 with full premium FSI availability. Notified Transit-Oriented Development corridors along major Chennai axes (Anna Salai, OMR sections) can permit FSI up to 6.075 — a special override above the standard 3.25 cap. Outside CMDA, the Directorate of Town and Country Planning (DTCP) administers TNCDBR through municipal corporations (Coimbatore CCMC, Madurai, Trichy, Salem) with the same FSI tables but no TOD bonus outside notified corridors. In village panchayat areas, FSI is generally capped at 1.5 for residential and premium FSI is typically not extended; layout approval still requires DTCP, not the panchayat president.
FSI is the conversion factor between land cost and project capacity. A higher FSI means more saleable area per rupee of land, which makes high-FSI plots disproportionately valuable. When evaluating two plots at similar prices, the one with higher permissible FSI almost always wins on per-saleable-square-foot economics — but only if you compute the *correct* FSI for the plot. A 600 sq ft plot fronting a 10m road cannot legally support a 25m high-rise no matter what FSI a back-of-envelope calc returns. Always pull the plot’s actual road width, frontage, zoning classification, and any premium FSI eligibility before finalizing a price.
This is a v1 calculator focused on the most common case. It does not model: corner plots (dual frontage setbacks), aquifer recharge zones (FSI capped at 0.80, ground coverage 40%), CRZ-I/II/III coastal restrictions, heritage precincts (notified in CMDA areas with reduced FSI), TOD corridor FSI overrides up to 6.075, industrial zones (Section 36 separate schedule), or TDR (Transfer of Development Rights) receiving plots. For projects in any of these categories, treat this output as a starting estimate and confirm with a TN urban planning consultant or the CMDA / DTCP planning office before commitments.
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