FAR is an area budget. Not a building shape.
The arithmetic is simple. The design question is not. A floor area ratio tells you how much counted floor area relates to a lot—not where that area fits, how tall it can be, or whether the proposed use is allowed.
3 floors × 8,000 sq ftTwo-thirds of the lot as a footprint
4 floors × 6,000 sq ftOne-half of the lot as a footprint
Start with the right two areas
FAR divides the floor area counted under the zoning rules by the applicable lot area. In New York City, for example, the Zoning Resolution defines both floor area and zoning lot; those definitions matter as much as the ratio itself. Do not assume the assessor’s parcel area, a leasing schedule, and a zoning calculation use interchangeable measurements.
- Identify the jurisdiction, zoning district, and applicable overlays.
- Record the lot-area source and the boundary used in the calculation.
- Read the local definition of counted floor area, including exclusions.
Work the arithmetic before the massing
For a hypothetical 12,000-square-foot lot with an assumed maximum FAR of 2.0, the area allowance is 24,000 square feet. Three equal 8,000-square-foot floors and four equal 6,000-square-foot floors reach the same total. They have different footprints and different design consequences. This is an arithmetic comparison, not a determination that either arrangement is permitted.
Separate FAR from lot coverage
FAR compares counted floor area across levels with the lot. Lot coverage generally concerns the portion of the lot covered by buildings, subject to the local definition. In the simplified example, an 8,000-square-foot footprint occupies two-thirds of a 12,000-square-foot lot; a 6,000-square-foot footprint occupies one-half. Neither percentage is an assumed allowable coverage limit.
Find the constraint that actually binds
An area allowance is only one input to a site concept. Lay out setbacks and any easements, then test height, access, parking, service space, and the intended program. A scheme can use less than the allowed floor area and still be impractical. Conversely, an appealing massing can depend on an entitlement that has not been established.
- Keep base allowances separate from proposed bonuses or discretionary approvals.
- Track zoning floor area separately from gross construction and rentable areas.
- Compare each option using the same lot boundary and counting method.
Make the feasibility handoff useful
Carry the equation, area schedule, rule reference, and scenario drawing together. If a colleague cannot reproduce the numerator and denominator, the ratio alone is not a useful handoff. Record what changes between options: footprint, number of levels, program, circulation, and the assumptions that still need investigation.
Primary references
Use these sources as a starting point, not a project-specific determination. Check the full context, applicable rules, and current project assumptions before using a result.