FAR Is the Single Most Important Number for Understanding How Much Building a Site Can Support
Floor Area Ratio (FAR) is a zoning control tool that limits the total floor area of a building relative to the site area. FAR is calculated as the ratio of total gross floor area (GFA) to the total site area: FAR = GFA ÷ Site Area. A site with a 10,000 SF area and a FAR of 2.0 can support a maximum of 20,000 SF of floor area - this could be a single two-story building covering the entire site, a four-story building covering half the site, or any combination that totals 20,000 SF. FAR is the zoning mechanism that controls the density of development (how much built space relative to land area) on urban sites. Understanding FAR and being able to calculate it quickly is a fundamental site analysis skill tested on the ARE PA exam.
What Counts Toward FAR
FAR calculations include gross floor area of all floors of the building. What counts toward FAR varies by jurisdiction, but generally: all occupied floor area at all levels (above and below grade); mechanical equipment floors (typically, though some jurisdictions exempt mechanical floors if height-limited); parking above grade (typically counts toward FAR; below-grade parking typically excluded). Exemptions vary by jurisdiction but may include: below-grade parking; mechanical penthouses below a height threshold; covered but unenclosed areas (arcades, canopied areas); bonus FAR provisions for providing amenities (public plazas, affordable housing, transit connections); corner lots may have modified FAR calculations.
FAR Examples
| Site Area | Zoning FAR | Maximum GFA | Possible Building |
|---|---|---|---|
| 10,000 SF | 1.0 | 10,000 SF | 1-story full coverage or 2-story 50% coverage |
| 10,000 SF | 3.0 | 30,000 SF | 3-story full coverage or 6-story 50% coverage |
| 10,000 SF | 10.0 | 100,000 SF | 10-story full coverage or 20-story 50% coverage (high-rise) |
FAR in the Context of Other Zoning Controls
FAR does not operate in isolation - it is one of several zoning controls that together define the building envelope. Height limits, setbacks, lot coverage (maximum footprint as a percentage of site), open space requirements, and parking minimums all interact with FAR to define the maximum achievable building form. In some cases, the building that maximizes FAR use is constrained by other factors - a 10-story building that maximizes a FAR of 10.0 may be prohibited by a 5-story height limit, reducing achievable FAR to 5.0 regardless of the FAR allowance.
Key Exam Points
- FAR = Gross Floor Area ÷ Site Area.
- FAR controls total floor area relative to site; more FAR = more building density allowed.
- What counts: all occupied floors at all levels; above-grade parking typically counts.
- Common exemptions: below-grade parking, mechanical penthouses, bonus provisions for amenities.
- FAR interacts with height limits, setbacks, and lot coverage - the binding constraint may be something other than FAR.
AREprep's PA site analysis content covers FAR calculation, zoning controls, site analysis, and how multiple zoning parameters interact to define the maximum achievable building program - giving ARE PA candidates the zoning analysis skills the exam tests in site analysis scenario questions where candidates must determine what the zoning allows, calculate FAR, and identify which constraint is binding on the project's development potential.
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