Calculate FSI (floor space index, or FAR) from total floor area and plot area, or find the floor area or plot area from an FSI, in m², sq ft or sq yd.
- All Construction Calculators
- Gross Floor Area Calculator
- Floor to Area Ratio Calculator
- Land to Building Ratio Calculator
Floor Space Index Formula
- FSI = Floor Space Index (dimensionless ratio)
- TFA = Total Floor Area across all floors (sq ft or sq m)
- TA = Total Area of the plot (sq ft or sq m)
FSI is a dimensionless ratio. At an assumed FSI of2.0, a10,000sqft plot gives20,000sqft total counted floor area arithmetically. Four equal5,000sqft floors or two equal10,000sqft floors have the same ratio; setbacks, coverage, height and other site rules may prevent either design.
What is a Floor Space Index?
Floor Space Index (FSI), Floor Area Ratio (FAR), and Gross Plot Ratio express total counted floor area relative to plot area. They are used as development-intensity measures, but definitions and exclusions vary by jurisdiction. A ratio alone does not establish permission or building height.
FSI does not directly specify building height. Two plots can share the same FSI yet produce very different buildings: one could be a slender tower covering a small footprint, another a low podium covering the full lot. Height limits and setback rules typically work alongside FSI to shape the final built form.
Checking Local FSI Limits
FSI limits are site-specific. The following locations illustrate why a city-wide number cannot replace the applicable zoning map, use, counted-area definition and current rules. No numerical city benchmark is used by this calculator.
| City / Zone | Site-specific limit | Verification needed |
|---|---|---|
| New York City (CBD) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Singapore (city-wide) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Hong Kong (urban) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Mumbai (residential) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Mumbai (commercial) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Delhi (Master Plan) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
| Bangalore (residential) | Check current local rules | Confirm the exact site, use, overlays, area definitions and applicable permissions. |
A simple ratio does not establish housing costs, approval or buildability. For example, Singapore URA guidance explains that plot ratio is an upper bound that may not be achievable because other site and technical constraints also apply.
Illustrative FSI Arithmetic (Not Zoning Limits)
| Scenario | Assumed FSI | Floor area on a1,000m² plot |
|---|---|---|
| Illustrative example1 | 0.5 | 500m² |
| Illustrative example2 | 1 | 1000m² |
| Illustrative example3 | 2 | 2000m² |
| Illustrative example4 | 3 | 3000m² |
| Illustrative example5 | 5 | 5000m² |
| Illustrative example6 | 8 | 8000m² |
Base FSI, Premium FSI, and TDR
Some planning systems distinguish a base ratio from separately authorized bonuses or transferred rights. These mechanisms and their conditions are local; the calculator accepts only the ratio you enter and does not grant or combine permissions:
- Base FSI is a basic ratio defined under the applicable local plan; fees and other requirements may still apply.
- Premium FSI, where a local scheme provides for it, may allow additional floor area subject to charges, caps and approval.
- Transfer of Development Rights (TDR) can transfer eligible development capacity where a local scheme authorizes it. Receiving sites, caps, credits and conditions must be checked under that scheme.
Where local rules expressly allow additions, an approved effective ratio may incorporate base, bonus or transferred components. Do not add them automatically or assume they can all be used together. Other site controls still apply.
FSI vs FAR: Same Concept, Different Names
FSI, FAR and plot ratio share the basic division of counted floor area by plot area. Regulatory definitions of the numerator, denominator, exclusions and bonuses can differ, so use quantities that follow the same applicable rules.
