How is FSI calculated in commercial zoning?

FSI (Floor Space Index)—also known as FAR (Floor Area Ratio)—is calculated in commercial zoning to determine the maximum allowable built-up area on a parcel of land. It defines how much floor space can be developed relative to the size of the plot, and is a key factor in zoning compliance, density planning, and investment feasibility.

Formula to Calculate FSI

FSI = Total Built-Up Area / Plot Area

• Total Built-Up Area includes all constructed floor area (across all floors), excluding open-to-sky areas, unless otherwise stated by the local building code
  
• Plot Area is the gross area of the land parcel under consideration

Example Calculation

Let’s assume:

• Plot Area = 10,000 square feet
  
• FSI Allowed = 2.5
  

Maximum Built-Up Area = Plot Area × FSI
= 10,000 sq ft × 2.5
= 25,000 sq ft

This 25,000 sq ft can be distributed vertically over multiple floors depending on:

• Height restrictions
  
• Setback requirements
  
• Parking norms and open space mandates

Components Considered in FSI Calculation

• Included:
  
  • Internal usable spaces (commercial shops, office floors)
    
  • Staircases, lift cores, corridors (in most codes)
    
• Excluded (varies by jurisdiction):
  
  • Balconies, basements (if non-commercial use), terraces
    
  • Parking areas, service ducts, fire escapes (if exempt under local regulations)

Importance in Commercial Development

• Directly affects project scale, leasable area, and revenue potential
  
• Influences design decisions like number of floors, building footprint, and layout
  
• Higher FSI enables denser, vertical developments and can significantly boost land value

Variation by Zoning and Location

• Urban commercial zones often permit higher FSI (e.g., 3.0–5.0)
  
• Suburban or low-density commercial areas may have restricted FSI (e.g., 1.0–2.0)
  
• Cities may offer bonus FSI for:
  
  • Transit-oriented development (TOD)
    
  • Inclusion of public amenities
    
  • Green or sustainable building certifications
    

Transferable Development Rights (TDR)