Calculate maximum buildable floor area and unused development rights from lot size and FAR.
Maximum zoning floor area — not all building space counts toward FAR (cellars, mechanical deductions, and open terraces are typically excluded; see ZR 12-10). Bonuses (inclusionary housing, plazas) can raise the effective FAR. Confirm your district's FAR and lot area on ZoLa or by looking up the property below.
FAR = Maximum Allowed Floor Area / Lot Area
Or inversely: Maximum Allowed Floor Area = Lot Area x FAR
A 2,500 sq ft lot in an R6 district (FAR 2.43 for residential):
A 10,000 sq ft lot in a C4-6 district (FAR 10.0 commercial, 10.0 residential):
Not all building space counts toward FAR. The Zoning Resolution (ZR 12-10) defines "floor area" as the sum of gross areas of all floors, with specific exclusions:
If your building uses less FAR than allowed, the difference is unused development rights (commonly called "air rights"). These rights have monetary value and can potentially be transferred to adjacent lots through zoning lot mergers.
Unused FAR = Allowed FAR - Built FAR
Example: 5,000 sq ft lot in R7A (FAR 4.0). Building has 12,000 sq ft of floor area.
FAR = Maximum Floor Area / Lot Area. Find your zoning district on ZoLa, look up the permitted FAR, and multiply by your lot area. The result is the maximum building floor area allowed.
The highest base FAR in NYC is 18.0, found in certain C5/C6 high-density commercial districts in Midtown Manhattan. With bonuses, effective FAR can be even higher.
This is an estimate. Look up any NYC address for the actual assessed value, tax class, zoning, and FAR — free, no account needed.