Floor Area Ratio Calculator uses FAR = gross floor area ÷ lot area to estimate build ratio, zoning capacity, limit used, lot coverage, and remaining areas from your lot, GFA, footprint, and FAR limit.
Ratio
sq ft
sq ft
Calculated Floor Area Ratio
1.20 FAR
Proposed Build Ratio vs Lot Size
Zoning Capacity
15,000 sq ft
Max Allowed FAR
1.50
Lot Size Base
10,000 sq ft
Absolute maximum gross floor area permitted on this lot by zoning.
Proposed Utilization
80.00% Limit Used
Proposed GFA
12,000 sq ft
FAR Status
Compliant
Percentage of the maximum allowable zoning capacity your proposed building utilizes.
Lot Coverage
30.00%
Building Footprint
3,000 sq ft
Unbuilt Open Area
7,000 sq ft
The percentage of the land physically covered by the building footprint.
Development Potential
3,000 sq ft
Remaining Capacity
3,000 sq ft
Floor Equivalents
1.0 Floors
Remaining buildable area you can add before hitting the maximum FAR limit.
FAR Zoning Note
Definitions vary strictly by local zoning codes. Many municipalities exclude basements, garages, and mechanical shafts from the Gross Floor Area calculation. Always consult local regulations.
Floor Area Ratio Calculator — How It Works
This Floor Area Ratio Calculator computes your project's FAR from two core inputs — the total lot area and the proposed gross floor area — then compares that result against the maximum FAR permitted in your zoning district. The tool also returns zoning capacity, lot coverage, open area, remaining buildable area, and floor equivalents, giving you a complete picture of how your proposed building sits against the site's regulatory envelope.
Floor area ratio is a dimensionless zoning metric that expresses how much total building floor area is proposed relative to the lot it sits on. A FAR of 1.50 means the total floor area equals one and a half times the lot area. Local zoning ordinances set maximum FAR limits that vary significantly by zone type — residential, commercial, mixed-use, or industrial — and by jurisdiction.
FAR definitions are not universal. Municipalities differ in what counts as gross floor area — some exclude basements, covered parking, mechanical rooms, or balconies; others include them. Always cross-reference your results with the specific definitions in your local zoning code before making any design or permitting decision.
FAR Formula Reference
Floor Area Ratio
FAR
=
Gross Floor Area
Lot Area
Core ratio — dimensionless result
Zoning Capacity
Max Floor Area
=
Lot Area
×
Max Allowed FAR
Maximum gross floor area permitted by zoning
FAR Limit Used
Limit Used
=
Calculated FAR
Max Allowed FAR
× 100
Expressed as a percentage of the zoning limit
Lot Coverage
Lot Coverage
=
Building Footprint
Lot Area
× 100
Ground-level coverage as a percentage of lot
What Each Input Means
Measurement System
US Customary · Metric
Controls all area units in the calculator. Select US Customary to work in square feet and acres; select Metric to work in square metres and hectares. Switching recalculates all displayed values.
Total Lot Area
sq ft · acres · sq m · hectares
The full land area of the parcel being evaluated. Enter the area in your selected unit. The tool converts acres (× 43,560) or hectares (× 10,000) to base area units internally before computing FAR.
Max Allowed FAR
Dimensionless ratio — from zoning schedule
The maximum floor area ratio permitted for your zoning district, as stated in your local zoning ordinance or land use schedule. This is the upper compliance threshold the calculator checks your project against.
Proposed Gross Floor Area
sq ft or sq m (all floors combined)
The total enclosed floor area of the proposed building across all floors. This is the numerator of the FAR formula. Enter the sum of all floor levels included in your local code's GFA definition — not just the footprint.
Proposed Footprint Area
sq ft or sq m (ground coverage only)
The ground-level area physically covered by the building's outermost walls. Used to compute lot coverage percentage and to calculate floor equivalents. Separate from gross floor area — a two-storey building with a 3,000 sq ft footprint has a GFA of roughly 6,000 sq ft.
Understanding Your Results
Primary
Calculated Floor Area Ratio
The FAR for your proposed project: GFA divided by lot area. Shown as a decimal. This is the number that must not exceed the Max Allowed FAR for zoning compliance.
Capacity
Zoning Capacity
The absolute maximum gross floor area the zoning allows on this lot (Lot Area × Max Allowed FAR). The upper ceiling for total buildable space under current zoning.
Utilisation
Proposed Utilization
The percentage of the maximum zoning capacity consumed by the proposed GFA. 80% means you are using 80% of the allowable buildable area. Below 100% indicates remaining headroom.
Status
FAR Status
Displays Compliant when Calculated FAR ≤ Max Allowed FAR, or Over Limit when the proposal exceeds the zoning threshold. A warning alert appears when over the limit.
Coverage
Lot Coverage
Building footprint as a percentage of total lot area. Distinct from FAR — lot coverage is a ground-plane measurement. Many jurisdictions impose a separate maximum lot coverage limit.
Coverage
Unbuilt Open Area
Lot area not covered by the building footprint (Lot Area − Footprint). Shown when the footprint is smaller than the lot. Switches to Footprint Excess if the footprint input exceeds the lot area.
Warning
Footprint Excess
Displayed only when the entered footprint area exceeds the total lot area. Triggers a design warning alert. Indicates a likely data entry error or an infeasible footprint size.
Potential
Development Potential
The headline figure on the Development Potential card — the absolute remaining capacity (sq ft or sq m) available before the FAR limit is reached, or the excess GFA amount if already over the limit.
Potential
Remaining Capacity
Square footage or square metres you can still add to the design before reaching the maximum allowed FAR. Equals Zoning Capacity minus Proposed GFA, shown only when the project is compliant.
Over Limit
Excess GFA
The amount by which the proposed gross floor area exceeds the zoning capacity. Only shown when FAR Status is Over Limit. Represents the area that must be removed for the design to comply.
Reference
Floor Equivalents
Remaining capacity ÷ current footprint — a reference figure showing how many additional footprint-sized floors the remaining FAR headroom could theoretically support. This is not a guaranteed number of legally buildable stories; setbacks, height limits, and structural requirements apply separately.
Worked Example
Example Inputs
Total Lot Area
10,000 sq ft
Max Allowed FAR
1.50
Proposed Gross Floor Area
12,000 sq ft
Proposed Footprint
3,000 sq ft
Step-by-Step Calculations
1
FAR = 12,000 ÷ 10,000 = 1.20
Calculated FAR is 1.20 — the proposed GFA divided by the lot area.
2
Zoning Capacity = 10,000 × 1.50 = 15,000 sq ft
Maximum allowable gross floor area under this zoning limit.
3
Limit Used = (1.20 ÷ 1.50) × 100 = 80.00%
The proposed design uses 80% of the maximum zoning capacity — 20% remains.
4
Lot Coverage = (3,000 ÷ 10,000) × 100 = 30.00%
The building footprint covers 30% of the lot; 7,000 sq ft is open land.
5
Remaining Capacity = 15,000 − 12,000 = 3,000 sq ft
3,000 sq ft of additional gross floor area is still permissible under this FAR limit.
6
Floor Equivalents = 3,000 ÷ 3,000 = 1.0 Floors
The remaining 3,000 sq ft equals one additional footprint-sized floor — a reference figure only.
✓ FAR Compliant — Remaining Capacity: 3,000 sq ft
The proposed FAR of 1.20 is below the 1.50 zoning limit, so the project is within compliance based on these inputs. The design has 3,000 sq ft of remaining FAR headroom, which the calculator reports as 1.0 floor equivalent relative to the 3,000 sq ft footprint. Compliance under other zoning controls — height, setbacks, lot coverage maximums, parking — requires separate review.
Important Zoning Limitations
FAR definitions are set locally and vary significantly between municipalities and zoning districts. The areas counted — or excluded — from gross floor area differ from one code to the next. This calculator computes FAR from the areas you enter; it does not apply your jurisdiction's specific GFA exclusions automatically.
Common elements that local codes may exclude from, or treat differently within, the gross floor area calculation:
!
Basements
Often excluded if below finished grade; varies widely
!
Garages & Parking Areas
Structured or surface parking may be fully or partially excluded
!
Mechanical & Utility Rooms
HVAC, electrical, and plant rooms frequently exempted
!
Stairwells & Elevator Shafts
Vertical circulation shafts may be excluded per floor or altogether
!
Balconies & Terraces
Some codes include open balconies partially; others exclude entirely
!
Covered Outdoor Areas
Covered walkways, arcades, or colonnades differ by ordinance
!
Accessory Structures
Detached garages, sheds, or ADUs may count separately or not at all
!
Attic & Mezzanine Space
Treatment depends on finished/unfinished status and ceiling height rules
References & Authoritative Sources
US Codes
The largest public repository of US municipal codes. Search by city or county to find the zoning ordinance, FAR schedules, and gross floor area definitions that apply to your specific parcel.
ICC
Publisher of the International Building Code (IBC) and International Zoning Code (IZC), which define floor area, gross floor area, and occupiable space. Most US jurisdictions adopt IBC with local amendments.
Planning
The APA provides zoning practice guides, policy briefs, and a zoning practice publication covering FAR, density bonuses, and development standards used across US municipalities.
Atlas
An open-data project mapping zoning districts across US states. Useful for locating your parcel's zoning designation before looking up the applicable FAR limit in the local ordinance.
HUD
HUD publishes research on zoning regulations, land use controls, and their effects on housing supply — including analysis of FAR limits across jurisdictions. Relevant for residential development projects.