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Floor Area Ratio Calculator

Construction

Calculate the Floor Area Ratio (FAR) for a lot by dividing total building floor area by lot area. Used for zoning compliance and maximum buildable area checks.

Reviewed by the thecalcu.com team · Last updated July 8, 2026

1001,000,000
1001,000,000

Floor Area Ratio (FAR)

1.5
Lot Area
4,000

This calculator computes your Floor Area Ratio (FAR), Lot Area from the values you enter.

Inputs
Total Building Floor AreaLot Area
Outputs
Floor Area Ratio (FAR)Lot Area

What is a Floor Area Ratio?

A Floor Area Ratio Calculator computes FAR, the ratio of a building's total floor area to the size of the lot it occupies, a key zoning metric used by municipalities to control development density. FAR is calculated simply by dividing total building floor area (summed across all stories) by the lot's land area, and most residential and commercial zoning districts set a maximum allowable FAR that any new construction must respect.

Understanding your lot's FAR early in a project helps you avoid designing a building that exceeds local zoning limits, which can force costly redesigns or variance applications. If you're also evaluating overall site layout, the Rectangle Fence Perimeter Calculator and Square Yards Calculator can help with related lot-dimension planning.

Why Use a Floor Area Ratio Calculator?

Zoning codes typically cap FAR to control neighborhood density, light access, and infrastructure load, and exceeding the limit during design can trigger a rejected permit application or require a lengthy variance process. This calculator gives you a fast way to check whether a proposed building size fits within your lot's zoning envelope before committing to detailed architectural plans.

It's particularly useful during early feasibility studies, plugging in a proposed total floor area against your known lot size instantly tells you whether the project is even zoning-compliant before spending money on design work.

Who Should Use This Calculator?

Architects and building designers use this calculator during schematic design to confirm a proposed building program fits within zoning FAR limits. Real estate developers use it during site feasibility analysis to estimate how much buildable floor area a lot can support before acquisition. Homeowners planning additions use it to check whether an expansion would push their property over the local FAR cap. Zoning consultants and permit expediters use it as a quick first-pass check before deeper zoning research. Real estate investors evaluating a lot's development potential use FAR alongside lot size to estimate maximum achievable building size.

What Insights Does the Floor Area Ratio Calculator Give You?

The Floor Area Ratio (FAR) is the primary result, a single number representing the density of building floor area relative to lot size. Compare this figure against your municipality's published maximum FAR for your zoning district to check compliance. The Lot Area output echoes back your input for quick reference alongside the FAR figure, useful when comparing multiple lot or design scenarios side by side. If your calculated FAR exceeds the zoning limit, you'll need to reduce total floor area, pursue a variance, or reconsider the number of stories in your design.

How to use this Floor Area Ratio calculator

  1. Enter your Total Building Floor Area in square feet, sum the floor area across all stories of the proposed or existing building.
  2. Enter your Lot Area in square feet.
  3. Review the Floor Area Ratio (FAR) result.
  4. Compare the result against your municipality's maximum allowed FAR for your zoning district.
  5. Adjust total floor area or reconsider your design if the calculated FAR exceeds the local limit.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The calculator uses the standard zoning FAR formula:

FAR = Total Building Floor Area ÷ Lot Area

Worked example: For a building with 6,000 sq ft of total floor area on a 4,000 sq ft lot:

FAR = 6,000 ÷ 4,000 = 1.5

This means the building's total floor area is one and a half times the lot's area, achievable, for example, with a two-story building covering about 3,000 sq ft of ground footprint (75% lot coverage) or a taller building on a smaller footprint.

Frequently Asked Questions

What is Floor Area Ratio (FAR)?
Floor Area Ratio (FAR) is a zoning metric that expresses the relationship between a building's total floor area and the size of the lot it sits on, calculated by dividing total building floor area by lot area. A FAR of 1.0 means the building's total floor area equals the lot size, while a FAR of 2.0 means the building has twice as much floor area as the lot, typically achieved with multiple stories.
How is FAR different from lot coverage?
Lot coverage measures only the building's footprint (ground-floor area) as a percentage of the lot, while FAR accounts for the total floor area across all stories. A two-story building with a small footprint can have a high FAR but low lot coverage, since its total floor area is spread over multiple floors on a small ground footprint.
What is a typical maximum FAR for residential zoning?
Maximum allowable FAR varies widely by municipality and zoning district, single-family residential zones commonly allow FAR limits between 0.3 and 0.6, while dense urban commercial zones can permit FAR values of 5.0 or higher. Always check your local zoning ordinance for the specific FAR cap that applies to your lot.
How do I find my lot's maximum allowed FAR?
Your local municipal planning or zoning department publishes FAR limits by zoning district, often available through an online zoning map or code lookup tool. Some jurisdictions also apply different FAR limits based on lot size, corner lot status, or proximity to specific streets.
Does a basement count toward FAR?
This varies by jurisdiction, some zoning codes exclude fully below-grade basements from FAR calculations, while others count any finished habitable space regardless of grade level. Check your specific municipal zoning definition of 'floor area' before finalizing a design based on FAR limits.
How does FAR affect how many stories I can build?
For a fixed lot size and building footprint, a higher allowed FAR generally permits more stories, since each additional floor adds to the total floor area used in the FAR calculation. A architect or designer uses the maximum allowed FAR to determine how much total floor area, and therefore how many stories, a project can include.
What's the difference between FAR and building height limits?
FAR limits total floor area regardless of how it's distributed vertically, while height limits cap how tall a structure can physically be. A project must satisfy both constraints simultaneously, a design with room under the FAR limit might still be blocked by a height cap, and vice versa.
Can I increase my lot's effective FAR through zoning exceptions?
Some municipalities offer FAR bonuses or variances for features like affordable housing units, green building certification, or public amenities, though these programs vary significantly by jurisdiction. Consult your local planning department about any applicable bonus programs before assuming a higher FAR is achievable.
How do I use this calculator during early project planning?
Enter your lot area and a proposed total building floor area to check the resulting FAR against your municipality's zoning limit before finalizing architectural plans, helping you avoid designing a building that later fails a zoning review.
Also known as
FAR calculatorfloor area ratio zoning calculatorfloor to area ratio calculatorbuilding floor area ratio calculatorlot coverage ratio calculator