What is Floor Area Ratio?
Floor Area Ratio (FAR), also known as Floor Space Index (FSI) or Floor Space Ratio (FSR), is a zoning and urban planning metric that describes the relationship between a building's total usable floor area and the total area of the lot on which it stands. It is one of the most fundamental tools used by municipalities to regulate building density and control urban development.
A higher FAR indicates denser development, while a lower FAR indicates more open space relative to built space. For example, a FAR of 1.0 means the total floor area equals the lot area, which could be achieved by a single-story building covering the entire lot or a two-story building covering half the lot.
FAR Formula
The total floor area includes all stories of a building. Some jurisdictions exclude certain areas such as basements, parking garages, mechanical rooms, and stairwells from the FAR calculation. Always check local building codes for specific exclusion rules.
FAR in Zoning Regulations
| Zone Type | Typical FAR Range | Description |
|---|---|---|
| Low-Density Residential | 0.2 – 0.5 | Single-family homes with large yards |
| Medium-Density Residential | 0.5 – 1.5 | Townhouses, small apartment buildings |
| High-Density Residential | 1.5 – 5.0 | Mid-rise and high-rise apartments |
| Commercial | 1.0 – 10.0 | Office buildings, retail centers |
| Central Business District | 5.0 – 25.0+ | Skyscrapers, dense urban cores |
Common FAR Values
- Suburban single-family: FAR of 0.2 to 0.4 is common, meaning only 20-40% of the lot is covered by building footprint.
- Urban mixed-use: FAR of 2.0 to 4.0 allows for multi-story buildings with ground-floor retail and upper-floor residential.
- Manhattan (NYC): Some areas allow FAR up to 15.0 or higher, enabling the construction of tall skyscrapers on relatively small lots.
Worked Example
A developer has a 10,000 sq ft lot and wants to build a 2-story building with 2,500 sq ft per floor:
This means the building uses 50% of the allowable development intensity if the maximum FAR is 1.0, or 20% if the maximum FAR is 2.5.
Frequently Asked Questions
What areas are typically excluded from FAR calculations?
Common exclusions include below-grade basements, parking garages, mechanical rooms, elevator shafts, stairwells, and sometimes balconies and terraces. Specific exclusions vary by jurisdiction, so always consult local zoning codes.
Can FAR be increased through bonuses?
Yes, many cities offer FAR bonuses for including affordable housing units, providing public amenities like plazas or parks, achieving green building certification, or preserving historic structures. These incentives allow developers to build more floor area than the base FAR would permit.
What is the difference between FAR and lot coverage?
Lot coverage refers to the percentage of the lot covered by the building footprint (ground floor only), while FAR accounts for the total floor area across all stories. A tall, narrow building could have low lot coverage but high FAR.
How does FAR affect property value?
Higher FAR generally increases property value because it allows more buildable floor area on the same lot. Developers pay premiums for lots with higher allowable FAR, especially in urban areas where land is scarce and expensive.