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FSI / FAR Calculator

Permissible built-up area from FSI and ground coverage. FSI limits total floor area and ground coverage limits the footprint, and it is the two together that decide how tall a building can be.

Also called: far calculator, floor space index.

sq ft
%
ft
Permissible built-up area
9,000

9,000 sq ft permissible on a 4,000 sq ft plot at an FSI of 2.25. With 50% ground coverage that is about 4.5 floors of 2,000 sq ft each, reaching roughly 50 ft.

Total FSI available
2.25
Maximum footprint
2,000
Floors possible
4.5
Approximate height
50
Built-up on base FSI alone
7,000
Open space on the plot
2,000
How this is calculated
Method and background

How this is calculated

FSI, called FAR in some jurisdictions, is the ratio of total constructible floor area to plot area. Ground coverage separately caps how much of the plot the building may occupy. Dividing the permissible area by the permitted footprint gives the number of floors, which is why a high FSI with a low ground coverage produces towers and the reverse produces low sprawl. Many cities sell additional FSI above the base entitlement, which is included here as a separate input.

FSI caps total floor area; ground coverage caps the footprint, and together they set the height
g
Ground coverage
FSI
Floor space index

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a 4,000 sq ft plot

Plot area
4,000 sq ft
Permissible FSI
1.75
Additional purchasable FSI
0.5
Maximum ground coverage
50%
Floor to floor height
10 ft

Permissible built-up area9,000

4000 x 2.25, over a 2000 sq ft footprint

Open this example

full ground coverage means floors equal FSI

Plot area
4,000 sq ft
Permissible FSI
2
Additional purchasable FSI
0
Maximum ground coverage
100%
Floor to floor height
10 ft

Permissible built-up area8,000

boundary

Open this example

Method and limits

What it assumes

  • A simple rectangular development with uniform floor plates.

What it deliberately does not model

  • Setbacks, height limits, parking requirements and fire rules all reduce what is actually buildable.
  • FSI definitions vary: some jurisdictions exclude parking, balconies or service areas from the count.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Is FSI the same as FAR?
Yes, they are the same ratio under different names. Indian codes usually say FSI and American ones FAR.
Why does ground coverage matter if FSI is fixed?
Because it sets the footprint. The same FSI with half the coverage means twice the floors, which changes the building entirely.