Estimate FAR based on total floor area and lot size
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Founder & CEO, Toolraxy
Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.
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Floor Area Ratio commonly abbreviated as FAR is one of the most important numbers in real estate development, urban planning, and zoning compliance. It measures the relationship between a building’s total floor area and the size of the lot it sits on, determining how intensively a property can be developed. A Floor Area Ratio Calculator helps you compute this ratio instantly by dividing your building’s total floor area by the lot size, then comparing the result against your local zoning maximum to tell you whether your project is within limits, near maximum, or exceeding what is allowed. Whether you are a homeowner planning an addition, an investor evaluating a development site, or an architect verifying compliance, Toolraxy provides a free, client-side calculator that makes FAR calculation simple and transparent.
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Enter your building’s total floor area in square feet. This is the sum of all floors, not just the building footprint.
Enter your lot size in square feet.
Enter the maximum FAR allowed by your zoning district, if known. Enter 0 if there is no limit.
Click Calculate. The tool displays your floor area, lot size, calculated FAR, maximum FAR allowed, whether your project is within or exceeds the limit, and the maximum buildable area for your lot.
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This Floor Area Ratio Calculator applies the standard FAR formula: FAR = Total Floor Area รท Lot Size.
Floor Area Ratio Calculation:
FAR = Total Building Floor Area รท Lot Size
For example, a 2,500 sq ft building on a 5,000 sq ft lot has a FAR of 0.5. A three-story building with 1,000 sq ft on each floor (3,000 sq ft total) on the same lot would have a FAR of 0.6. The result is a dimensionless number that expresses building density.
Maximum FAR Comparison:
The user enters the maximum FAR allowed by local zoning. If the calculated FAR is below the maximum, the project is within limits. If above, the project exceeds limits and may require a variance or redesign.
Buildable Area Calculation:
Buildable Area = Lot Size ร Maximum FAR
This shows the maximum total floor area that can be built on the lot under current zoning. If no maximum FAR is entered (0), the buildable area is displayed as “Unlimited.”
FAR Status Classification:
The calculator classifies the result into three categories:
Exceeds limit: FAR is above the maximum
Near maximum: FAR is between 70% and 100% of the maximum
Within limit: FAR is below 70% of the maximum
This provides a quick visual indication of how close the project is to the zoning threshold. The classification uses dynamic highlightsโred for exceeding, yellow for near maximum, and green for well within.
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Consider a developer evaluating a 5,000 sq ft lot with a maximum FAR of 1.0 and a planned building with 4,200 sq ft of total floor area:
FAR: 4,200 รท 5,000 = 0.84.
Maximum FAR: 1.0.
FAR status: 0.84 is between 0.70 (70% of 1.0) and 1.0, so the project is “Near maximum.”
Buildable area: 5,000 ร 1.0 = 5,000 sq ft.
Remaining buildable area: 5,000 – 4,200 = 800 sq ft.
The result shows “
Near maximum (FAR = 0.84)” with a yellow highlight. The developer understands the project uses 84% of the available FAR and could add approximately 800 more square feet before hitting the zoning limit.
If the same lot had a planned building of 5,500 sq ft, the FAR would be 1.1 exceeding the 1.0 maximum. The calculator would show “
Exceeds limit (FAR = 1.10)” with a red highlight and advise reducing floor area or seeking a variance.
How accurate is this FAR calculator?
The calculation is precise: FAR = Total Floor Area รท Lot Size. The accuracy of the result depends on the accuracy of your inputs. For zoning compliance, always verify your building’s gross floor area definition and your lot size with official records and local zoning regulations.
What counts as total floor area?
Total floor area typically includes all enclosed, heated, and habitable space across all floors, measured to the outside face of exterior walls. Basements, garages, attics, and mechanical rooms may be excluded depending on local codes. Verify with your zoning department.
Can I calculate FAR for a multi-story building?
Yes. Add together the floor area of every story to get the total floor area, then divide by the lot size. The calculator accepts any total floor area, regardless of how many stories the building has.
What does it mean if my FAR is near the maximum?
The calculator flags projects between 70% and 100% of the maximum FAR. This indicates you are using most of the allowed development potential with limited room for expansion.
How do I find my local maximum FAR?
Check your property’s zoning district and the municipal zoning code. Many cities publish zoning maps and FAR tables online. You can also contact your local planning or zoning department.
Does the calculator account for zoning exemptions or bonuses?
No. Some municipalities offer FAR bonuses for affordable housing, green building features, or preservation. The calculator uses the maximum FAR you enter without adjustments.
Does the calculator store my property data?
No. All calculations run entirely in your browser. No personal or property data is saved or transmitted.
Can I share my FAR calculation?
Yes. Use the Copy button to copy all results, or the Share button to send a summary that includes your FAR and zoning status.
Is this calculator a substitute for professional zoning analysis?
No. This tool provides basic FAR calculations for informational purposes. For development decisions, consult a zoning attorney, urban planner, or your local planning department.
What is the difference between FAR and FSI?
FAR (Floor Area Ratio) and FSI (Floor Space Index) are the same concept expressed differently. In the US, FAR is typical a decimal like 1.0 or 2.5. In India, the UK, and other countries, FSI is used a percentage like 100% or 250%. FSI รท 100 = FAR.
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