Calculate Floor Area Ratio (FAR)

How to Calculate Floor Area Ratio (FAR)

Floor Area Ratio (FAR) is an essential zoning metric that helps determine a building's bulk relative to its land size. To perform the calculation, you need the gross floor area (GFA) of the building and the total lot size.

Gathering Your Data

Start by determining the gross floor area, which is the total square footage enclosed by the building's external walls. Next, assess the total lot size, which is the land area where the property is situated. Lot size can sometimes be tricky to measure depending on the property’s shape.

Calculating FAR

With your data at hand, use the straightforward formula for FAR: FAR = GFA / Total Lot Size. This ratio, typically shown as a decimal, indicates how high or large a building can be relative to the size of the lot it occupies. For example, a building with a GFA of 20,000 sq. ft standing on a 5,000 sq. ft lot results in a FAR of 4.0.

Determining Maximum Allowable FAR

To find the maximum FAR allowed on a parcel of land, multiply the lot size by the zoning area's maximum FAR regulation: Maximum Allowable FAR = Total Lot Size * Maximum FAR. This calculation helps developers understand the largest size building permissible on their lot under current zoning laws.

Understanding and calculating FAR is crucial for compliance with local zoning rules and for optimally planning property development. The calculation aids in maintaining a balance between building size and land use intensity, particularly in regions with high zoning regulations.

How to Calculate Floor Area Ratio (FAR)

Understanding the Floor Area Ratio (FAR) is essential for developers and builders to ensure compliance with local zoning regulations. FAR represents the ratio of a building's total floor area to the size of its plot, expressed in decimal form, not a percentage.

Step-by-Step Guide to Calculating FAR

To determine the FAR, divide the Gross Floor Area (GFA) of the building by the Total Lot Size. The formula is straightforward: FAR = GFA / Total Lot Size. This calculation provides a decimal value indicating the density level, which can vary considerably depending on local zoning laws.

Example Calculations

For a practical understanding, consider a building with 20,000 sq. ft. on a 5,000 sq. ft. lot. The calculation would be FAR = 20,000 / 5,000 = 4.0. Similarly, for a building in New York City with 12,000 sq. ft. and a lot size of 1,400 sq. ft., the FAR would be approximately 8.6.

Calculating Maximum Allowable FAR

To predict the potential expansion or development of a property, multiply the Total Lot Size by the maximum FAR allowed under current zoning rules. Use the formula: Maximum Allowable Floor Area = Total Lot Size * Max. Floor Area Ratio (FAR).

By understanding and applying these calculations, developers can plan projects that are both compliant and optimally designed for the given property space, ensuring safety and adherence to local standards.

Examples of How to Calculate FAR

Example 1: Single Lot Development

To calculate FAR, divide the total area of all floors in the building by the area of the lot. If a building has 4,000 sq ft of floor space and sits on a 2,000 sq ft lot, its FAR is 4000 / 2000 = 2.

Example 2: Multi-building Complex

For developments with multiple buildings, sum the floor areas of all buildings. Divide by the lot area. If two buildings have 3,000 sq ft and 4,000 sq ft, on a 5,000 sq ft lot, the FAR is (3000 + 4000) / 5000 = 1.4.

Example 3: Inclusions and Exclusions

Confirm what the local zoning code includes or excludes in floor area calculations (e.g., basements, attics). If only the main floors are included, exclude basement and attic areas from your total floor area before calculating FAR.

Example 4: Building Additions

For building additions, add the area of the new structure to the existing floor area. Re-calculate against the original lot size. If adding 1,500 sq ft to an original 3,500 sq ft building on a 2,000 sq ft lot, the new FAR is (3500 + 1500) / 2000 = 2.5.

Example 5: Different Floor Area Ratios by Zone

Different zones may have different FAR limits. Calculate your project’s FAR and verify against local regulations to ensure compliance. If your area has a max of FAR 2 and your calculation exceeds this, consider redesigning to meet local requirements.

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