Floor Area Ratio Calculator
Enter your lot size and total floor area to get the Floor Area Ratio (FAR), also called the Floor Space Index (FSI). Switch to "Max buildable area" mode to find how much floor area your zoning allows, or use "Footprint and floors" mode to estimate FAR from building dimensions. All three modes support square feet and square metres and update instantly as you type.
Formula
Worked example
A 10,000 ft² lot has a building with 25,000 ft² of total floor area: FAR = 25,000 / 10,000 = 2.5. If local zoning allows FAR 3.0, the maximum buildable floor area is 10,000 x 3.0 = 30,000 ft², leaving 30,000 - 25,000 = 5,000 ft² of remaining allowance.
What is floor area ratio?
Floor Area Ratio (FAR), also called Floor Space Index (FSI) or Plot Ratio, is the ratio of a building's total floor area to the area of the lot it sits on. A FAR of 2.0 means the building contains twice as much floor space as the land beneath it, which could be achieved with a two-storey building covering the full lot, a four-storey building covering half the lot, or any other combination that totals twice the lot area. FAR is the primary lever that zoning codes use to control how densely a neighbourhood is built. Higher FAR limits allow taller or bulkier buildings; lower limits enforce lower-density, more open development. Municipalities set FAR limits district by district to balance growth, infrastructure capacity, sunlight, parking demand, and neighbourhood character.
How to use this calculator
Choose the calculation mode that matches your goal. In "Compute FAR" mode, enter the total lot area and the gross floor area of the building to find the FAR. In "Max buildable area" mode, enter the lot area and the FAR limit from your local zoning ordinance; the calculator returns the maximum total floor area you can build. Optionally enter any existing floor area to see how much remaining capacity is still available on the lot. In "Footprint and floors" mode, enter the building footprint (the area it covers on the ground) and the number of storeys; the calculator estimates the total floor area and the resulting FAR, along with the site coverage ratio. Toggle between square feet and square metres at any time and results update instantly.
FAR vs site coverage vs setbacks
FAR, site coverage and setback requirements work together to shape a building envelope. FAR caps the total floor area across all storeys. Site coverage (sometimes called building coverage or lot coverage) caps the percentage of the lot that the building footprint can occupy. Setback rules define how far the building must sit from property lines, roads and neighbours. A building can have a relatively high FAR by stacking floors while maintaining a small footprint, provided the site coverage and setback limits are also respected. Understanding all three constraints together is essential for feasibility analysis and preliminary design.
FAR in zoning and real estate
FAR is central to commercial real estate valuation because it directly determines how much rentable or saleable area can be built on a parcel. Developers compare the as-of-right FAR (the maximum permitted without a variance) against the as-built FAR of an existing structure to identify underutilised sites with remaining development potential. In dense urban markets, unused FAR allowance can even be transferred to adjacent parcels through transferable development rights (TDR) schemes, creating a market for air rights. When evaluating a site, always check whether the zoning FAR refers to gross floor area (all floors including stairs, lifts and mechanical rooms) or net floor area (occupied space only), as definitions vary by jurisdiction.
Typical FAR ranges by zoning type
| Zoning type | Typical FAR range | Description |
|---|---|---|
| Rural / agricultural | 0.01 - 0.10 | Very sparse development, mostly open land |
| Single-family residential (large lot) | 0.10 - 0.50 | Detached homes on generous plots |
| Single-family residential (standard) | 0.40 - 1.00 | Typical suburban neighborhoods |
| Multi-family / low-rise residential | 0.75 - 2.00 | Duplexes, townhouses, low-rise flats |
| Suburban commercial / mixed-use | 1.00 - 3.00 | Strip malls, low-rise offices, mixed retail |
| Urban mid-rise | 2.00 - 5.00 | Mid-rise apartments, offices, urban mixed-use |
| Urban high-rise / downtown core | 5.00 - 15.00 | High-rise towers in dense city centers |
| Transit-oriented development (TOD) | 3.00 - 10.00 | Higher density around rail/transit hubs |
These are general benchmarks. Actual limits vary by city, district and local zoning ordinance.
Frequently asked questions
What is a good FAR for a residential building?
It depends on the neighbourhood context. A single-family home on a standard suburban lot typically has a FAR between 0.4 and 1.0. Low-rise multi-family buildings commonly fall between 1.0 and 2.5. FAR values above 3.0 are generally found in urban mixed-use or apartment districts. "Good" is whatever your local zoning allows and what is appropriate for the surrounding built environment.
Is FAR the same as FSI?
Yes. Floor Area Ratio (FAR) and Floor Space Index (FSI) are the same metric calculated the same way: total floor area divided by lot area. FAR is the term used most widely in North America; FSI is more common in South Asia (especially India), and "plot ratio" is used in parts of Europe and Australia. All three are dimensionless numbers representing the same ratio.
What counts as floor area in FAR calculations?
Jurisdictions differ, but gross floor area typically includes all enclosed floor space measured from the outer faces of exterior walls: habitable rooms, corridors, stairwells, lift shafts, mechanical rooms, parking garages and any below-grade floors. Some codes exclude basements, parking floors, covered outdoor terraces or roof plant rooms. Always check your local ordinance definition before comparing FAR values across different cities.
How do I find the allowed FAR for my property?
The allowed FAR is set by the local zoning ordinance. Look up your property's zoning designation on the municipal zoning map (usually available on the city or county planning department's website), then look up that designation in the zoning code to find the FAR limit. Many cities also have an online parcel search tool that displays the zoning for a specific address. If you cannot find it online, contact the local planning or building department directly.
Can FAR be exceeded with a variance or special permit?
In many jurisdictions, yes. Developers can apply for a variance, rezoning, or planned development approval to build above the base FAR, often in exchange for providing affordable housing, public amenities, open space or transit improvements. These "density bonuses" are a common planning tool in cities that want to encourage specific types of development while managing overall density.
What is the difference between FAR and site coverage?
FAR measures total floor area across all storeys relative to the lot area; it does not restrict how much of the lot the building covers on the ground. Site coverage (or lot coverage) measures the building footprint as a percentage of the lot area, capping how much ground the structure occupies. A ten-storey building with a small footprint can have a high FAR and a low site coverage at the same time. Most zoning codes impose both limits independently.