Formula & Calculator
Building Floor Area Ratio (FAR)
Zoning ratio comparing a building's total constructed floor area (across all floors) to the size of its land plot.
Interpretation
Floor area ratio (FAR) = total floor area / plot area. Example: Plot 500 m², total floor area 1000 m² → FAR = 2.0. Regulates permissible built‑up area.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| FAR | Floor area ratio | |
| Total Floor Area | Sum of floor area on all stories | m2 |
| Plot Area | Land plot area | m2 |
What it means
Floor Area Ratio (FAR), also known as Floor Space Index (FSI) in some regions, is a zoning metric that controls the maximum allowable built‑up area on a plot relative to the plot size. It is calculated as the total floor area of all floors (including basements and mezzanines, depending on local rules) divided by the area of the plot. A FAR of 2.0 means that the total floor area can be twice the plot area, which typically allows two stories of full coverage or four stories with 50% coverage. FAR is used by municipalities to manage population density, infrastructure load, and urban form. It affects the design and height of buildings and influences property values. Developers use FAR to maximise profit within regulatory limits. Architects and planners must adhere to FAR to obtain building permits. The concept is central to urban planning and is a key factor in sustainable city development.
Worked example
Floor Area Ratio – Two Examples
Real‑World| Parameter | Value |
|---|---|
| Total floor area | 300 m² |
| Plot area | 200 m² |
| Parameter | Value |
|---|---|
| Total floor area | 900 m² |
| Plot area | 400 m² |
Common mistakes
- Total floor area: Sum of the area of all floors (including basements, mezzanines) but excluding open areas, balconies, etc., as per local definitions.
- Plot area: The total land area, excluding any common areas if it is a multi‑unit development.
- Permissible FAR: Set by local building codes – do not exceed it.
- Different definitions: Some authorities include or exclude certain spaces (e.g., parking, mechanical rooms) – check your local regulation.
- FAR vs. FSI: FAR (floor area ratio) and FSI (floor space index) are often used interchangeably.
Applications
The Floor Area Ratio (FAR) is the ratio of the total floor area of a building (sum of all floors) to the area of the plot on which it stands. It is a key planning control used by municipalities to regulate building density and urban sprawl. Architects and developers use FAR to determine the maximum buildable area on a given site, influencing the building height and footprint. The FAR affects natural light, ventilation, and traffic generation. By calculating FAR, designers can ensure that the proposed development meets local zoning codes, avoids over‑development, and respects the character of the neighbourhood. It also helps in feasibility studies and in comparing different design options.
- Urban planning and zoning compliance
- Building massing and feasibility studies
- Site development and land‑use optimisation
- Design of multi‑storey buildings and high‑density housing
- Assessment of environmental and traffic impacts
Frequently Asked Questions
FAR is the ratio of total built‑up floor area (sum of all floors) to the plot area: FAR = Total Floor Area / Plot Area. It controls the density of development and is a key zoning parameter.
- Confusing FAR with building coverage ratio – building coverage is the footprint area, not total floor area.
- Not including all floors – basement, mezzanine, and attic spaces may or may not count, depending on the code.
- Using the wrong plot area – the plot area is the land area, not the built‑up area.
- Misinterpreting FAR as a percentage – FAR is a dimensionless number (e.g., 2.5), not a percentage.
Maximum Total Floor Area = Plot Area × FAR. For example, a 500 m² plot with FAR 2.0 allows up to 1000 m² of floor area.
Low‑density: 0.5‑1.0; medium‑density: 1.0‑2.5; high‑density: 3.0‑6.0 or more. It varies greatly by city and zoning district.
For a given FAR, a larger footprint allows lower height; a smaller footprint requires taller building. FAR doesn't directly limit height but limits total floor area.
They are the same concept. FSI is used in some countries (e.g., India), while FAR is more common in the US and other regions. Both are the ratio of floor area to plot area.
FAR regulations often exclude certain areas (e.g., balconies, parking, mechanical rooms) from the floor area calculation. Consult the local building code for exclusions.
Higher FAR allows more people or businesses per unit of land, increasing demand for infrastructure (roads, water, sewage). Planners use FAR to control population density.
Sum the floor areas of all uses (residential, commercial, etc.) and divide by the plot area. The same FAR applies to the entire building.
Exceeding FAR is a zoning violation. Penalties may include fines, demolition of illegal structures, or denial of occupancy permits. Always check with the local planning department.