This Floor Space Index calculator finds your FSI (also called FAR) from the total built-up area and the plot area. Enter both figures above to get the ratio and check it against your local limit.
How is FSI calculated?
FSI (FAR) = Total built-up floor area ÷ Plot area Allowed floor area = Plot area × Permitted FSI
Total built-up area is the sum of every floor’s area; the plot area is the land the building sits on.
Example calculation
For a plot of 1,000 ft² with 2,500 ft² of total floor area:
- FSI = 2,500 ÷ 1,000 = 2.5
If your zone permits an FSI of 2.0, you could build 1,000 × 2.0 = 2,000 ft² total.
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Frequently Asked Questions
What is Floor Space Index (FSI)?
FSI, also called Floor Area Ratio (FAR), is the total built-up floor area divided by the plot area. An FSI of 2 means you can build twice the plot area.
How do I calculate FSI?
Divide the total floor area of all stories by the plot area. A 2,500 sq ft build on a 1,000 sq ft plot gives an FSI of 2.5.
What is a good FSI value?
Permitted FSI is set by local zoning, not by preference. Denser urban zones allow higher FSI; always check your municipal limit before designing.