FSI Calculator API: how much can I build in Tamil Nadu

Example

Request

curl -X POST https://verified.realestate/api/v1/tools/fsi_calculator \
  -H "Authorization: Bearer $LANDLENS_KEY" \
  -H "Content-Type: application/json" \
  -d '{"plot_area":2400,"frontage":40,"depth":60,"road_width":30,"unit":"feet"}'

Responsereal answer

{
  "ok": true,
  "status": "ok",
  "data": {
    "found": true,
    "max_fsi": 2,
    "achievable_fsi": 1.705,
    "permissible_built_up_sqm": 445.93,
    "permissible_built_up_sqft": 4800,
    "achievable_built_up_sqm": 380.22,
    "achievable_built_up_sqft": 4093,
    "building_floors": "S+3/G+2",
    "floors_count": 3,
    "max_height_m": 14,
    "front_setback_m": 3,
    "rear_setback_m": 1.5,
    "side_setback_one_m": 1.5,
    "side_setback_other_m": 1.5,
    "footprint_sqm": 126.74,
    "plot_coverage_pct": 56.84,
    "osr_sqm": 0,
    "is_high_rise": false,
    "premium": {
      "applicable": true,
      "usable": false,
      "reason": "Premium FSI is open to this plot (up to 2.6), but after the setbacks and the floors its height allows the plot cannot build past the base FSI, so buying it adds no floor area.",
      "premium_fsi": 2.6,
      "bonus_percent": 30,
      "charge_percent": 50
    },
    "rules": [
      {
        "topic": "Front setback",
        "rule": "Rule 35(1) Table E(i): Existing road width 9-18m requires 3m front setback",
        "working": "Existing road width: 9.144m in 9-18m range → Front setback: 3m",
        "source": "G.O. Ms. No. 16 (2020), Rule 35(1) Table E(i), Page 3"
      }
    ],
    "unit_given": "feet"
  },
  "credits_charged": 0
}

A real answer from the API for a 40 by 60 foot plot on a 30 foot road, trimmed for length: one of eight rules is shown, and the building size, the rest of premium and the basis are left out.

What it returns

One call, one plot. Read the base figures, then premium, then rules for the citations.

Field	What it holds
`max_fsi, achievable_fsi`	The FSI the rules allow and the FSI the plot can actually reach after setbacks and height.
`permissible_built_up_sqm / _sqft, achievable_built_up_sqm / _sqft`	Built-up area at the maximum FSI, and what can actually be built.
`building_floors, floors_count, max_height_m`	The floors (for example S+3/G+2) and the height limit.
`front_setback_m, rear_setback_m, side_setback_one_m, side_setback_other_m`	The setbacks in metres.
`building_width_m, building_depth_m, footprint_sqm, plot_coverage_pct`	The building that fits inside the setbacks, and how much of the plot it covers.
`osr_sqm, housing_units, is_high_rise`	Open space reservation, the homes assumed, and whether it is worked as a high rise.
`premium`	Whether premium FSI applies, whether it adds floor area here, the premium FSI, extra area, chargeable area and the charge as a share of guideline value.
`rules[]`	Each figure's rule: topic, rule, working and the government order and page.
`notes, basis`	Why a high rise fell back, the CRZ limits applied, and the rules the whole answer rests on.

Inputs

The JSON body of the POST is the arguments. Send the plot area, frontage, depth and road width. Add zone flags only when a zone check or the owner says so; never guess them.

Argument	Type	What to send
`plot_area`required	number	Plot area, in square metres (or square feet when unit is feet)
`frontage`required	number	Width of the plot along the road, in metres (or feet)
`depth`required	number	Depth of the plot away from the road, in metres (or feet). For an irregular plot, the largest rectangle that fits.
`road_width`required	number	The width of the road the plot faces today. The rules read the existing width.
`road_widening`	number	Depth of the plot the planning authority will take for a proposed road widening, in metres (or feet). Optional.
`unit`	string: metres, feet	metres (the default) or feet, for every length and area sent.
`housing_units`	integer	Homes planned. More than 16 makes it a large development. Default 8.
`commercial_area`	number	Commercial floor area planned, in SQ.M whatever the unit. Over 300 sq.m makes it a large development. Default 0.
`priority`	string: builtup, height, coverage	builtup (the most floor area, default), height (the most floors) or coverage (the largest footprint).
`high_rise`	boolean	Plan a high-rise building (over 19.5 m). Needs a 12 m road and room for 7 m setbacks; otherwise the answer falls back to a non high-rise building and says why.
`cba`	boolean	The plot is in a Continuous Building Area
`ews`	boolean	The plot is in an Economically Weaker Section area or a natham
`aquifer`	boolean	The plot is in the aquifer recharge area
`redhills`	boolean	The plot is in the Redhills lake catchment
`crz`	string: none, crz1, crz2, crz3	none, crz2 or crz3. A CRZ-I plot allows no new building and is refused.
`tod`	boolean	Within 500 m of the centre line of a Chennai Metro Rail corridor (Rule 30(5)(ii)), or of the MRTS (Chennai Beach to Velachery, Velachery to St. Thomas Mount) or the suburban rail corridors Chennai Beach to Vandalur, Chennai Beach to Minjur and Chennai Central to Thiruninravur (Rule 30(5)(iii), G.O. 15/2024): premium FSI charge halved
`zones`	array	The same zone flags as a list, for a form: any of cba, ews, aquifer, redhills, tod.

Code

Set LANDLENS_KEY to your key. In an AI app, connect https://verified.realestate/mcp once and ask in plain words instead. In Postman, download this API's collection, import it (File, Import) and set apiKey.

curl -X POST https://verified.realestate/api/v1/tools/fsi_calculator \
  -H "Authorization: Bearer $LANDLENS_KEY" \
  -H "Content-Type: application/json" \
  -d '{"plot_area":2400,"frontage":40,"depth":60,"road_width":30,"unit":"feet"}'

import os, requests

r = requests.post(
    "https://verified.realestate/api/v1/tools/fsi_calculator",
    headers={"Authorization": f"Bearer {os.environ['LANDLENS_KEY']}"},
    json={
        "plot_area": 2400,
        "frontage": 40,
        "depth": 60,
        "road_width": 30,
        "unit": "feet"
    },
    timeout=15,
)
body = r.json()
print(body["status"], body["credits_charged"], body["data"])

const res = await fetch("https://verified.realestate/api/v1/tools/fsi_calculator", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.LANDLENS_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "plot_area": 2400,
    "frontage": 40,
    "depth": 60,
    "road_width": 30,
    "unit": "feet"
  }),
});
const body = await res.json();
console.log(body.status, body.credits_charged, body.data);

How much can I build on a 40 by 60 foot plot on a 30 foot road in Chennai? Is premium FSI worth buying?

Your AI works out the FSI under TNCDBR 2019 and cites each rule. It is free.

Responses

Every answer has the same envelope. What status can say for this call:

status	What it means
`ok`	The plot was worked out.
`not_found`	A figure was zero or missing, the plot could not be worked out, or the plot is CRZ-I where no new building is allowed. Nothing is charged.
`invalid_args`	plot_area, frontage, depth or road_width was missing. Nothing ran.
`free_limit_reached`	The account has used its free calls for the hour or the day. retry_after says how many seconds to wait; paid calls keep working.

Where the data comes from

Register

The Tamil Nadu Combined Development and Building Rules 2019, as amended to G.O. Ms. No. 69 of 2024, and the CRZ Notification 2019 where a coastal zone is given.

Coverage

Plots anywhere in Tamil Nadu. The zone flags you send decide which special rules apply; the calculator does not read a map.

How current

The rule tables follow the amendments through G.O. 69 of 2024, and each figure cites the order it comes from.

How we read it

The same engine that runs Build Scope and the FSI calculator page: height and floors from the road width, setbacks from the rule tables, the largest building that fits inside them, then premium FSI on top of the base FSI. Stilt and basement parking floors do not count towards FSI (Rule 29).

Who uses it

Owners and buyers

Know how many square feet a plot allows before buying it or signing a joint development.

Architects

Check the base and premium FSI and the setbacks before drawing, with the rule for each.

Property platforms

Show buildable area on plot listings from the plot's size and road width.

Limits and good practice

One rectangular plot. For an irregular plot use the largest rectangle that fits.
The figures are indicative. The planning authority decides on the drawn plan.
Zone flags change the answer and are not read from a map here. Run zone_check first if unsure.
Premium FSI is bought at a share of the guideline value; this gives the share, not the rupees.

Pricing

Free

The FSI calculator costs nothing. Free calls have their own allowance per hour and per day, counted across every key and connected app on the account. Credits come from the same LandLens wallet as the chat and the minis. How billing works.

Calling at volume?

Free calls have an hourly and daily allowance. For more than that, or a platform built on these registers, we set up limits and a plan to match.

WhatsApp 99961 29996

Questions

Is there an FSI calculator API for Tamil Nadu?

Yes. Send the plot area, frontage, depth and road width, and get the FSI, built-up area, floors, height and setbacks under TNCDBR 2019, each with its rule.

What is premium FSI and do I get it?

Extra FSI bought on a road at least 9 m wide, at a share of the guideline value. premium says whether it applies, how much, and whether the plot can actually use it after setbacks and height.

Can I send the plot in feet?

Yes. Set unit to feet and send lengths in feet and area in square feet. Commercial area stays in square metres.

How much does it cost?

It costs nothing, within the account's free call allowance.