Solve the floor area ratio of any building, find the maximum buildable area your zoning allows, or plan a footprint × floors massing — with sq ft, sq m, acre & hectare inputs. Also answers the international twin: Floor Space Index (FSI).
Three real scenarios, computed by the engine above. Each shows the full chain: inputs → gross floor area → FAR.
5,000 sq ft2,000 sq ft (two floors × 1,000 sq ft)2,000 ÷ 5,000 = 0.4 (40%) — Very low densityA low-density result typical of single-family zoning (commonly 0.3–0.5). Plenty of headroom under most residential caps.
4,000 sq ft; footprint 2,500 sq ft × 3 floors2,500 × 3 = 7,500 sq ft7,500 ÷ 4,000 = 1.875 (187.5%); lot coverage = 62.5%8,000 sq ft; remaining capacity 500 sq ftFits the zoning with 500 sq ft to spare — enough for a small rooftop addition, permits allowing.
6,000 sq ft7,500 sq ft7,500 ÷ 6,000 = 1.25 (125%) — Medium densityA medium-density result, comfortably inside typical multi-family ranges (0.5–2.0).
These two controls measure different dimensions. Lot coverage is the ground-floor footprint divided by lot area — how much land the building touches. FAR is the floor area of all levels divided by lot area — how much building the lot carries.
| Design on a 6,000 sq ft lot (3,000 sq ft footprint) | Lot coverage | Total floor area | FAR |
|---|---|---|---|
| 1 floor | 50% | 3,000 sq ft | 0.5 |
| 2 floors | 50% | 6,000 sq ft | 1 |
| 4 floors | 50% | 12,000 sq ft | 2 |
Coverage never moves while FAR doubles with each added floor. Check both against your zoning code — passing one does not imply passing the other.
| District type | Typical FAR range |
|---|---|
| Single-family residential | 0.3 – 0.5 |
| Multi-family residential | 0.5 – 2.0 |
| High-rise residential | 2.0 – 5.0 |
| Neighborhood commercial | 0.5 – 1.0 |
| Community commercial | 1.0 – 2.0 |
| Regional commercial | 2.0 – 4.0 |
| Mixed-use (low / medium / high) | 0.5–1.0 / 1.0–2.0 / 2.0–4.0 |
| Industrial (light / medium / heavy) | 0.3–0.5 / 0.5–1.0 / 1.0–2.0 |
| Central business district | 5.0 – 15.0+ |
Ranges compiled from published zoning references (see Sources in the build notes). They describe what districts commonly allow — your parcel's code is the only number that matters.
Floor Space Index (FSI) — the term used in India, the UK, and other countries — is the same ratio as FAR. An FSI of 1.5 is a FAR of 1.5; this calculator serves both terms.
FAR = gross floor area ÷ lot area (dimensionless)Max buildable area = lot area × allowed FARLot coverage = building footprint ÷ lot areaUnit handling: 1 acre = 43,560 sq ft and 1 sq ft = 0.09290304 sq m (exact, 1959 definitions); 1 hectare = 10,000 sq m. A half-acre lot, for instance, is 21,780 sq ft. Density classes shown by the calculator: very low below 0.5, low 0.5–1, medium 1–2.5, high 2.5–5, very high at 5 and above.
Floor area ratio (FAR) is a zoning metric that compares a building's total gross floor area to the size of the lot it sits on. The formula is FAR = gross floor area ÷ lot area, and the result is dimensionless. For example, a 30,000 sq ft building on a 20,000 sq ft lot has a FAR of 1.5 (150% of the lot area, medium density). Municipalities use FAR to control development density and intensity.
Three steps: (1) measure the lot area; (2) add up the gross floor area of every floor of the building; (3) divide floor area by lot area. Worked example: a building with 7,500 sq ft of floor area on a 6,000 sq ft lot gives FAR = 7,500 ÷ 6,000 = 1.25, or 125%. Mode 1 of the calculator above does this instantly, with acre and hectare lot inputs supported.
Multiply your lot area by the FAR your zoning district allows: max buildable = lot area × allowed FAR. For a 20,000 sq ft lot zoned at FAR 2.0, the ceiling is 40,000 sq ft of floor area. That total can take many shapes — four floors of 10,000 sq ft each, two floors of 20,000 sq ft, and so on — as long as the sum stays within the cap. Use mode 2 above and enter your existing floor area to see remaining capacity.
There is no universal good FAR — it depends on your zoning district. As a rough reference from zoning guides: single-family residential 0.3–0.5, multi-family 0.5–2.0, commercial 2.0–5.0, and central business districts 5.0–15.0+. A FAR that is normal in one district can be illegal next door, so always confirm the allowed FAR with your local planning department before designing or buying.
FAR counts every floor; lot coverage counts only the ground-floor footprint. Take a 3,000 sq ft footprint on a 6,000 sq ft lot: lot coverage is 50% no matter how tall you build, but FAR is 0.5 with one floor, 1 with two floors, and 2 with four floors. That is why a site can comply with coverage rules yet violate FAR limits — or vice versa.
Floor space index (FSI) is the same concept as FAR under a different name, used in India, the UK, and several other countries. FSI 1.5 and FAR 1.5 describe the identical ratio, so every mode of this calculator works as an FSI calculator too — just read the result as FSI.
In general, GFA is all enclosed, occupiable floor space across every level — rooms, hallways, lobbies, and mezzanines. Many codes exclude some combination of: underground or basement parking, mechanical and utility rooms, open balconies and terraces, and elevator or stair shafts. The exact inclusions vary by jurisdiction, which is why two cities can compute different FARs for the same building. Verify the GFA definition in your local code with the planning department.
Often it does not — many zoning codes exclude underground or structured parking garages from gross floor area, which is one reason developers put parking below grade. Surface parking, however, still consumes lot area and is limited by coverage and landscaping rules. Because the treatment of parking varies widely, confirm your local code before counting on an exclusion.
It means the total floor area may be up to twice the lot area. On a 10,000 sq ft lot, FAR 2.0 allows up to 20,000 sq ft of building — for example four floors of 5,000 sq ft or two floors of 10,000 sq ft. Expressed as a percentage, FAR 2.0 is 200%.
Yes. FAR above 1.0 is normal in dense districts — for instance, a 24,000 sq ft building on a 6,000 sq ft lot has a FAR of 4, meaning four times the lot area in floor space. Downtown commercial zones commonly allow FAR 5.0 to 15.0+, which is how high-rises fit on small parcels.
An over-FAR design generally cannot be permitted as drawn. Common paths are redesigning smaller, applying for a variance or rezoning, or — in cities that allow it — acquiring transferable development rights from another parcel. Building beyond the limit without approval risks fines and legal penalties. This calculator is a planning aid, not legal advice: confirm your options with the local planning department or a land-use professional.
It depends on your seat at the table. Developers and investors usually prefer higher FAR because it means more sellable or rentable area per dollar of land. Neighbors and planners may prefer lower FAR for light, air, traffic, and infrastructure capacity. Zoning sets the compromise for each district — the calculator tells you where a proposal lands, not which side is right.
A lot size calculator measures how big the land is — you enter dimensions and get acres or square feet (see our acreage calculator). This FAR calculator answers a zoning question instead: given the lot, how much floor space may be built on it. Use the land tools to measure the parcel, then this tool to test what the zoning lets you do with it.