Far Ratio Calculation

What is Floor Area Ratio (FAR)?

The Floor Area Ratio (FAR), also known as Floor Space Ratio (FSR) or Plot Ratio, is a measure used in zoning and urban planning to regulate the density of development on a piece of land. It is the ratio of a building’s total floor area (gross floor area) to the size of the piece of land upon which it is built. The Floor Area Ratio is expressed as a decimal number (e.g., 0.5, 1.0, 5.0). A higher Floor Area Ratio indicates a more densely built-up property.

For example, if a 10,000 sq ft lot is zoned with a maximum Floor Area Ratio of 0.5, then the total floor area of all buildings on that lot cannot exceed 5,000 sq ft (10,000 * 0.5). If the FAR is 2.0, the total floor area could be up to 20,000 sq ft, likely indicating a multi-story building.

Who should use it?

Real Estate Developers: To determine the maximum buildable area on a plot of land based on zoning regulations.
Architects and Planners: To design buildings that comply with local density rules set by the Floor Area Ratio.
Urban Planners: To control population density, manage infrastructure, and shape the character of neighborhoods.
Property Investors: To assess the development potential and value of land.
Homeowners: To understand restrictions on additions or new constructions on their property.

Common Misconceptions

FAR is the same as lot coverage: Lot coverage refers to the percentage of the lot area covered by the building’s footprint, while Floor Area Ratio considers the total floor area of all stories.
A high FAR always means a tall building: While often true, a high Floor Area Ratio can also be achieved by a building that covers a large portion of the lot with fewer stories.
FAR is the only density control: Other regulations like height limits, setbacks, and parking requirements also control development density alongside the Floor Area Ratio.

Floor Area Ratio (FAR) Formula and Mathematical Explanation

The formula for calculating the Floor Area Ratio is straightforward:

FAR = Total Floor Area / Lot Area

Where:

Total Floor Area: This is the sum of the gross floor area of all floors within all buildings on the lot, including basements (if counted by local code), mezzanines, and enclosed porches. It’s usually measured from the exterior walls. Specific inclusions/exclusions can vary by jurisdiction.
Lot Area: This is the total horizontal area of the land parcel on which the building(s) are located.

The Floor Area Ratio is a dimensionless quantity, as both areas are measured in the same units (e.g., square feet or square meters), which cancel out.

Variables Table

Variables used in the Floor Area Ratio calculation.
Variable	Meaning	Unit	Typical Range
Total Floor Area	The sum of the gross floor area of all stories in all buildings on the lot.	sq ft, sq m	100 – 1,000,000+
Lot Area	The total area of the land parcel.	sq ft, sq m, acres, hectares	1,000 – 1,000,000+
FAR	Floor Area Ratio (dimensionless)	None (ratio)	0.1 – 20+

Practical Examples (Real-World Use Cases)

Example 1: Suburban Single-Family Home

Lot Area: 8,000 sq ft
Total Floor Area of House (2 stories): 3,200 sq ft
Calculation: FAR = 3,200 / 8,000 = 0.4
Interpretation: The Floor Area Ratio is 0.4. If the local zoning allows a FAR of 0.5, the homeowner could potentially add another 800 sq ft of floor area (8,000 * 0.5 – 3,200 = 800), subject to other regulations like setbacks and height limits.

Example 2: Downtown Office Building

Lot Area: 20,000 sq ft
Total Floor Area of Building (10 stories): 150,000 sq ft
Calculation: FAR = 150,000 / 20,000 = 7.5
Interpretation: The Floor Area Ratio is 7.5, indicating a very dense development typical of a city center. The building’s total floor area is 7.5 times the area of the land it sits on.

How to Use This Floor Area Ratio (FAR) Calculator

Enter Total Floor Area: Input the combined gross floor area of all buildings on the lot into the “Total Floor Area of Building(s)” field. Ensure you use consistent units (e.g., square feet or square meters).
Enter Total Lot Area: Input the total area of the land parcel into the “Total Lot Area” field, using the same units as the floor area.
View Results: The calculator will automatically display the calculated Floor Area Ratio, along with the input values used.
Check the Chart: The bar chart visually compares the Lot Area and the Total Floor Area you entered.
Reset if Needed: Click the “Reset” button to clear the inputs and start with default values.
Copy Results: Use the “Copy Results” button to copy the FAR and input values to your clipboard.

How to read results:

The primary result is the Floor Area Ratio. A FAR of 1.0 means the total floor area equals the lot area. A FAR less than 1.0 means the floor area is less than the lot area, and greater than 1.0 means it’s more (likely a multi-story building).

Decision-making guidance:

Compare the calculated Floor Area Ratio to the maximum FAR allowed by local zoning regulations for that specific property. This will tell you if the current or proposed development is within legal limits or if there’s potential for more construction.

Key Factors That Affect Floor Area Ratio (FAR) Results & Usage

Zoning Regulations: Local municipal zoning ordinances are the primary determinant of the maximum allowable Floor Area Ratio for a specific parcel of land. Different zones (residential, commercial, industrial) will have different FAR limits.
Lot Size and Shape: The area of the lot directly influences the total buildable floor area for a given Floor Area Ratio. Irregular lot shapes might also affect usable space.
Building Height Limits: While FAR controls total floor area, height limits separately restrict how tall a building can be, influencing the number of stories and building footprint to achieve the allowed Floor Area Ratio.
Setback Requirements: Rules dictating how far buildings must be set back from property lines, roads, and other structures can limit the building footprint, which in turn affects how the total floor area allowed by the Floor Area Ratio can be distributed vertically.
Parking and Open Space Requirements: Zoning codes often mandate minimum parking spaces and open/green space, which can consume lot area and indirectly constrain the buildable area within the Floor Area Ratio limits.
Intended Land Use: The purpose of the development (e.g., single-family home, apartments, office, retail) often corresponds to different Floor Area Ratio allowances set by planners to manage density and infrastructure load.
Community Plans and Overlays: Specific neighborhood plans or overlay districts can impose additional or modified Floor Area Ratio restrictions or bonuses to encourage or discourage certain types of development.

Frequently Asked Questions (FAQ)

1. What does a Floor Area Ratio of 1.0 mean?: A Floor Area Ratio of 1.0 means the total floor area of the building(s) is equal to the total area of the lot. For example, a 10,000 sq ft lot could have a 10,000 sq ft building (either one story covering the whole lot, or two stories covering half, etc., subject to other rules).
2. How is Total Floor Area calculated for FAR?: Total Floor Area (or Gross Floor Area) typically includes the area of all floors measured from the exterior walls. However, local codes vary regarding the inclusion of basements, attics, garages, balconies, and mechanical spaces. Always check local definitions.
3. Can I build more than the FAR allows?: Generally, no. Building beyond the maximum allowed Floor Area Ratio would violate zoning codes. However, some jurisdictions offer bonuses or variances under specific conditions (e.g., providing public amenities).
4. Does FAR include parking garages?: It depends on local regulations. Sometimes underground parking or a certain portion of above-ground parking is excluded from the Floor Area Ratio calculation.
5. How does FAR relate to property value?: A higher allowable Floor Area Ratio generally increases the development potential of a property, which can lead to a higher land value, especially in urban areas.
6. Why do cities use FAR?: Cities use Floor Area Ratio to manage density, control the scale of development, ensure adequate light and air, and plan for infrastructure needs like traffic, utilities, and public services.
7. Is FAR the same everywhere?: No, Floor Area Ratio limits vary significantly between different cities, and even between different zones within the same city.
8. How do I find the allowed FAR for my property?: You can usually find the allowed Floor Area Ratio in your local municipality’s zoning code or by contacting the local planning or building department. It’s often specified in zoning maps and ordinances associated with your property’s zoning district.

Related Tools and Internal Resources

Zoning Laws Explained: Understand the basics of zoning regulations and how they impact property development, including the Floor Area Ratio.
Land Development Guide: A comprehensive guide to the land development process, where Floor Area Ratio plays a crucial role.
Building Permit Process: Learn about obtaining building permits, which requires adherence to FAR and other zoning rules.
Real Estate Investment Tools: Explore tools for real estate investors, where understanding the development potential via Floor Area Ratio is key.
Urban Planning Basics: An introduction to urban planning concepts, including density control through Floor Area Ratio.
Construction Cost Estimator: Estimate construction costs, which are related to the total floor area derived from the FAR.

Floor Area Ratio (FAR) Calculator

FAR Calculator

Calculation Results