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Calculate Floor Area Ratio (FAR/FSI/FSR), chargeable buildable area, lot coverage and minimum open space for zoning compliance. For architects and planners.
Calculate Floor Area Ratio (FAR) and lot coverage percentage for zoning and site planning. Enter your lot dimensions, building footprint, and floor areas to check compliance with local zoning regulations.
Have feedback? Report bugs, suggest features, or share your thoughts — we read them allWhat is Floor Area Ratio (FAR)?
Floor Area Ratio (FAR), also known as Floor Space Index (FSI) or Floor Space Ratio (FSR), is a key urban planning metric that measures the relationship between a building's total floor area and the size of the lot it sits on. A FAR of 1.0 means the total floor area equals the lot area. A FAR of 2.0 means the total floor area is twice the lot area, which could be a 2-story building covering the entire lot, or a 4-story building covering half the lot.
What is Lot Coverage?
Lot Coverage (also called Building Coverage or Site Coverage) is the percentage of a lot that is occupied by the building footprint. Unlike FAR, which considers all floors, lot coverage only looks at the ground-level footprint. Zoning codes typically limit lot coverage to ensure adequate open space, landscaping, parking, and stormwater management.
How to Use This Calculator
- Enter your total lot area and select the unit (sq ft, m², or acres).
- Enter the building footprint area (ground floor outline).
- Add the area for each floor of the building. Click 'Add Floor' for multi-story buildings.
- Optionally enter your local zoning FAR and lot coverage limits to check compliance.
- Click 'Calculate' to see your FAR, lot coverage, and detailed breakdown.
Formulas Used
FAR = Total Floor Area ÷ Lot Area
Lot Coverage (%) = (Building Footprint ÷ Lot Area) × 100
Max Buildable Area = Lot Area × FAR Limit
Remaining Area = Max Buildable Area − Chargeable Floor Area
Max Floors = Max Buildable Area ÷ Building Footprint
Chargeable FAR = (Total Floor Area − Excluded Area) ÷ Lot Area
Open Space (%) = 100 − Lot Coverage (%)
Common FAR Values by Zone
- Rural / Agricultural: 0.1 – 0.3
- Single-Family Residential: 0.3 – 0.7
- Multi-Family Residential: 1.0 – 3.0
- Neighborhood Commercial: 1.0 – 2.5
- Downtown Commercial: 3.0 – 10.0
- High-Density Urban Core: 10.0 – 25.0
Zoning & Planning Tips
- FAR limits vary significantly by zone: residential areas may be 0.5–1.5, while commercial districts can be 5.0–15.0.
- Lot coverage limits typically range from 25% to 80% depending on the zoning district.
- Some jurisdictions exclude basements, parking garages, or mechanical spaces from FAR calculations.
- Building setbacks, height restrictions, and lot coverage limits work together to shape building form.
- Higher FAR values indicate denser development and are common in urban centers.
- Always check your local zoning ordinance for specific FAR calculation rules and exemptions.
Common Applications
- Zoning compliance verification for building permits
- Feasibility studies for real estate development
- Architectural site planning and massing studies
- Urban density analysis and planning reviews
- Property value and development potential assessment
- Variance and rezoning application preparation
Frequently Asked Questions
Floor Area Ratio is a zoning metric that limits how much building floor area can be constructed on a given parcel of land. It is calculated as FAR = Total Gross Floor Area ÷ Lot Area. A 10,000 ft² lot with a 0.5 FAR allows up to 5,000 ft² of building floor area, regardless of how many stories. The American Planning Association and most U.S. municipal zoning codes use FAR as the primary density control tool, often together with height limits, setbacks, and open-space ratios. FAR values typically range from 0.1 in low-density residential to 12 or higher in dense urban centers like Manhattan.
Enter the gross floor area for every level as usual, then put any code-excluded space — below-grade parking, cellars, mechanical penthouses — into the 'Excluded Area (not in FAR)' field. The tool subtracts it to compute Chargeable GFA = Total Floor Area − Excluded Area, and reports Chargeable FAR = Chargeable GFA ÷ Lot Area. The Chargeable FAR becomes the headline figure and the one checked against your Max FAR Limit, because that is the number a zoning reviewer actually scores. The Gross FAR is still shown (muted) so you keep both the architectural total and the regulated total. The 'Area' input here is gross floor area (everything inside the exterior walls per the GFA definition), not net rentable or net usable area — convert net to gross before entering, or your FAR will read low. The Remaining Buildable Area is also recomputed on the chargeable basis so it reflects how much more chargeable floor area you may still add.
Most suburban and stormwater-regulated codes impose a minimum open-space (or pervious-area) ratio that is frequently the binding constraint — tighter than FAR or coverage. Enter your zoning minimum in 'Min Open Space (%)'. The tool computes Open Space (%) = 100 − Lot Coverage, compares it to your minimum, and shows a pass/fail Open Space Status badge with a progress bar. It also reports Required Open Space Area = Lot Area × (Min Open Space ÷ 100) so you can size lawns, planting, or pervious paving for permit submittal. Read the three verdicts together: Chargeable FAR must be at or below the FAR limit, Lot Coverage at or below the coverage limit, and Open Space at or above the minimum. A project can pass FAR and coverage yet fail open space, which is exactly the trap this check is meant to catch. Note this open-space figure is derived purely from building footprint coverage; driveways and surface parking that count against open space in some codes must be added to your footprint or handled separately.
FAR controls total floor area, coverage (or lot coverage) controls the percentage of the lot footprint that buildings may occupy, and height limits cap vertical dimension. A 0.5 FAR with 25 percent coverage on a 10,000 ft² lot means you can build either a 2-story 2,500 ft² footprint or a 5-story 1,000 ft² tower — both yield 5,000 ft² total. Modern zoning uses all three jointly to shape the building envelope. New York City's resolution and Chicago's Title 17 are good examples of layered controls. FAR alone does not determine massing; the interaction with other rules does.
Most zoning codes exclude unenclosed balconies, mechanical penthouses, parking garages below grade, attic space with less than 7 ft of headroom, and elevator shafts. New York's 1961 zoning resolution explicitly excludes mechanical floors and required affordable housing bonuses can add transferable FAR. San Francisco Planning Code Section 102 lists more than twenty exemptions. Always verify locally because basement exclusions in particular vary — some cities count any conditioned basement, others exclude all below-grade space. Misclassifying a half-cellar can push a project over the FAR limit and trigger redesign.
FAR bonuses let owners exceed base FAR in exchange for public benefits: affordable housing, plaza space, transit improvements, or historic preservation easements. New York's Inclusionary Housing Program grants up to 30 percent FAR bonus for permanently affordable units. TDR allows a sending parcel (often a historic landmark) to sell its unused FAR to a receiving parcel within a defined district, concentrating density where the city wants growth. Seattle's Downtown TDR program and Manhattan's South Street Seaport landmark district are textbook cases. Bonuses are legally negotiated and typically require zoning board approval.
International Building Code (IBC) Section 505 defines mezzanines as intermediate levels not exceeding one-third of the floor area below. Most zoning codes count mezzanine floor area toward FAR like any other floor. A double-height living room or atrium counts only the footprint once for FAR but may be limited by other rules (e.g., NYC requires a 'sky exposure plane' to prevent shadowing). Some cities exempt double-height retail lobbies as a bonus. Always check whether the FAR definition uses 'gross floor area' (everything inside the outer walls) or 'gross building area' (BOMA standard) — they can differ by 5–10 percent.
FAR directly determines how much rentable or saleable floor area a developer can build, which dominates project pro-forma calculations. A higher FAR generally raises land value because more buildable area amortizes the lot purchase. Manhattan's $10,000+/ft² land prices reflect FAR over 10; a similar Brooklyn lot at FAR 2 might trade for $400/ft². When buying land, the first due-diligence check is verifying the as-of-right FAR plus any available bonuses, plus historic district overlays or contextual zoning that may impose lower effective FAR than the underlying district allows.
Many zoning codes set minimum parking ratios per square foot of FAR — e.g., one space per 500 ft² of commercial floor area. Increasing FAR therefore increases the required parking count, which may consume on-site land or require a structured garage. Some progressive cities (Minneapolis, Buffalo, Sacramento) eliminated parking minimums to encourage density. Conversely, parking maximums are common near transit hubs. Loading-dock requirements scale similarly — over a certain FAR threshold, off-street loading berths become mandatory. Always check both minimum and maximum parking rules before assuming you can build to the full FAR cap.
Yes — split-zoning lots, planned unit developments (PUDs), and overlay districts can apply different FAR to different portions of one parcel. A corner lot spanning two zoning districts must compute FAR separately for each portion and may not transfer floor area across the line unless TDR is permitted. Overlay zones (historic, environmental protection, airport approach) can reduce the underlying FAR. PUDs let developers cluster density on one part of the site while preserving open space elsewhere, with overall FAR averaged. Always plot the actual zoning boundaries onto the survey before computing buildable area.
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