Floor to Area Ratio (FAR) Calculator
The Floor to Area Ratio (FAR) is a crucial zoning metric used to regulate building size relative to the size of the lot. It's calculated by dividing the total floor area of the building by the total area of the land parcel.
Use this calculator to determine the FAR for your property or project. Simply enter the Total Floor Area of the building and the Total Lot Area. Ensure both inputs use the same units (e.g., square feet, square meters).
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Understanding Floor to Area Ratio (FAR) & Calculation
What is Floor to Area Ratio?
FAR is a regulatory tool used in zoning to limit the amount of construction that can be built on a single parcel of land. It's expressed as a decimal number or a ratio (e.g., 0.5 or 5:1). A higher FAR generally permits denser development.
Why is FAR Important?
Municipalities use FAR to manage urban density, control the size and bulk of buildings, ensure adequate open space, prevent overcrowding, and manage the load on local infrastructure (like roads, water, sewer, schools). It's a key factor in urban planning and real estate development.
FAR Calculation Formula
The calculation is straightforward:
FAR = (Total Floor Area of Building) / (Total Area of Lot)
Remember to use the same units (like square feet or square meters) for both the Total Floor Area and the Total Lot Area.
What Counts Towards Total Floor Area?
This is defined by local zoning codes but typically includes the sum of the gross horizontal areas of all enclosed levels of a building, measured from the exterior faces of the exterior walls. Common exclusions (depending on local rules) might be basements, attics, garages, unenclosed balconies, or mechanical penthouses.
What Counts Towards Total Lot Area?
This is the total area of the legal parcel of land. It's typically determined from official property surveys or records and excludes areas within public streets or easements unless specifically included by local code.
FAR Examples
Click on an example to see the scenario and calculation:
Example 1: Small House on Large Lot
Scenario: A 2,500 sq ft house on a 10,000 sq ft lot.
Calculation: FAR = 2,500 sq ft / 10,000 sq ft = 0.25
Result: FAR = 0.25
Example 2: Larger House on Average Lot
Scenario: A 4,000 sq ft house on a 7,500 sq ft lot.
Calculation: FAR = 4,000 sq ft / 7,500 sq ft ≈ 0.5333
Result: FAR ≈ 0.5333
Example 3: Small Commercial Building
Scenario: An 8,000 sq ft commercial building on a 5,000 sq ft lot.
Calculation: FAR = 8,000 sq ft / 5,000 sq ft = 1.6
Result: FAR = 1.6
Example 4: Multi-Story Building (Metric Units)
Scenario: A building with a total floor area of 15,000 sq m on a 3,000 sq m lot.
Calculation: FAR = 15,000 sq m / 3,000 sq m = 5.0
Result: FAR = 5.0
Example 5: High-Rise Tower
Scenario: A 100,000 sq ft office tower on a 10,000 sq ft downtown lot.
Calculation: FAR = 100,000 sq ft / 10,000 sq ft = 10.0
Result: FAR = 10.0
Example 6: Calculating Allowed Floor Area
Scenario: A 12,000 sq ft lot is zoned for a maximum FAR of 0.6. What is the maximum allowed Total Floor Area?
Calculation: Maximum Floor Area = Maximum FAR * Lot Area = 0.6 * 12,000 sq ft = 7,200 sq ft.
Result: Maximum Allowed Floor Area = 7,200 sq ft. (The calculator itself calculates FAR *from* areas, but this shows the application).
Example 7: Using Acres (Conversion Needed)
Scenario: A 20,000 sq ft building on a 1-acre lot. Note: 1 acre = 43,560 sq ft.
Calculation: FAR = 20,000 sq ft / 43,560 sq ft ≈ 0.4591
Result: FAR ≈ 0.4591. (Ensure consistent units; convert acres to sq ft or sq m before using the calculator).
Example 8: Mixed-Use Building
Scenario: A mixed-use building with 5,000 sq ft commercial + 7,000 sq ft residential floor area on a 6,000 sq ft lot.
Calculation: Total Floor Area = 5,000 + 7,000 = 12,000 sq ft. FAR = 12,000 sq ft / 6,000 sq ft = 2.0
Result: FAR = 2.0
Example 9: Comparing to Zoning Limit
Scenario: A proposed building with 5,500 sq ft floor area on a 8,000 sq ft lot in a zone with a maximum FAR of 0.7.
Calculation: Calculated FAR = 5,500 sq ft / 8,000 sq ft = 0.6875
Result: Calculated FAR = 0.6875. Since 0.6875 is less than the maximum allowed 0.7, this design meets the FAR requirement.
Example 10: Very Low Density Development
Scenario: A 1,800 sq ft cabin on a 40,000 sq ft (approx 1 acre) wooded lot.
Calculation: FAR = 1,800 sq ft / 40,000 sq ft = 0.045
Result: FAR = 0.045. This indicates very low building intensity relative to the land size.
Frequently Asked Questions about FAR
1. What is a "good" or "typical" FAR?
There is no single "typical" FAR. It varies greatly depending on the zoning of the area. Low-density residential zones might have FARs below 0.5, while downtown commercial zones can have FARs of 10, 20, or even higher.
2. Does FAR restrict building height?
Not directly. FAR controls the *total floor area* relative to the lot. Height limits are usually governed by separate zoning regulations, although a high FAR often necessitates a taller building on a given lot size.
3. Does FAR account for lot coverage?
No. FAR deals with total floor area across all levels. Lot coverage (or building footprint) is a separate zoning regulation that limits the percentage of the land area that can be covered by the building's ground floor or main structure.
4. Are basements included in FAR calculations?
This depends entirely on local zoning codes. Some codes exclude unfinished or even finished basements, while others include them. Always check the specific regulations for your area.
5. Are garages or parking structures included in FAR?
Similar to basements, this is jurisdiction-specific. Attached or detached garages and dedicated parking levels might be excluded or partially included depending on the local rules and whether they are considered part of the "enclosed habitable space".
6. What units should I use for the inputs?
You can use any consistent units (like square feet, square meters, etc.) for both inputs. The resulting FAR is a unitless ratio. Just ensure *both* inputs use the *same* unit.
7. How can I find the allowed FAR for my property?
You need to consult the zoning regulations or zoning map provided by your local municipality, city planning department, or county government. This information is usually available on their website or by contacting their office.
8. Can I build a building with a higher FAR than allowed by zoning?
Generally, no. Building construction must comply with zoning regulations, including the maximum allowed FAR. Exceeding it would typically require obtaining a variance or a change in zoning, which is often a complex process.
9. What happens if my current building's FAR is higher than the newly adopted zoning allows?
Existing structures that comply with previous zoning but not current zoning are often considered "non-conforming." They can usually remain, but expanding them or rebuilding after significant damage may require compliance with the new, lower FAR.
10. Is the FAR calculated differently for different types of buildings (residential, commercial, industrial)?
The calculation method (Total Floor Area / Total Lot Area) is the same. However, zoning codes assign different *maximum allowed* FAR values to different zoning districts (e.g., R1 for single-family residential, C2 for commercial, M1 for light industrial), reflecting the desired density and intensity of use for that area.
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