The Dwelling Unit Factor (ZR 23-52): How Many Units You Can Build

After City of Yes, NYC uses one dwelling unit factor, 680, across all residence districts, which makes the unit math simpler but easy to get wrong if you work from older references.

The rule in one line

For buildings containing multiple dwelling residences, the maximum number of dwelling units is the maximum residential floor area permitted on the zoning lot divided by the dwelling unit factor. Since City of Yes for Housing Opportunity (last amended December 5, 2024), that factor is 680 in every residence district from R1 to R12, and a fraction of three-quarters or more counts as one more unit (ZR 23-52).

• The count is based on the maximum residential floor area permitted, not on the floor area you actually build. Building smaller does not lower the unit cap, and building bigger units does not raise it.
• It applies to developments, enlargements, and existing buildings that increase their number of dwelling units (ZR 23-51).
• It does not apply to single- or two-family residences, and it does not apply to rooming units (ZR 23-51).
• Any given floor area is counted only once in meeting the floor area requirements (ZR 23-51).

Where there is no dwelling unit factor

ZR 23-52 lists the cases with no applicable factor at all:

• Developments or enlargements of residences in special density areas. ZR 12-10 defines these as the Manhattan Core (Manhattan Community Districts 1 through 8) and the Special Downtown Brooklyn District.
• Qualifying senior housing, which ZR 12-10 defines as affordable independent residences for seniors or long-term care facilities.
• Conversions of any non-residential building, or part of one, to residences inside special density areas, and, outside special density areas, conversions of community facility buildings, or parts of buildings containing community facilities, to residences.

Where a zoning lot mixes residential uses with and without a factor, the floor area not subject to a factor is excluded before dividing. Shared floor area, such as a lobby, is split between the uses in proportion to the floor area each occupies on the zoning lot (ZR 23-52).

Maximum units on a 10,000 sq ft lot

Standard residential FAR from ZR 23-21 (R4, R5) and ZR 23-22 (R6B to R10). Qualifying affordable or senior housing and qualifying residential sites have higher FARs, and qualifying senior housing has no factor. Special purpose districts can change these rules.

Worked examples

• R6B, 5,000 sq ft lot: 5,000 x 2.00 = 10,000 sq ft. 10,000 / 680 = 14.71. The fraction 0.71 is under three-quarters, so the maximum is 14 units (ZR 23-22, 23-52).
• R7A, 10,000 sq ft lot: 10,000 x 4.00 = 40,000 sq ft. 40,000 / 680 = 58.82. The fraction 0.82 is three-quarters or more, so the maximum is 59 units.
• R7A with UAP: UAP developments are not on the no-factor list, so the factor still applies. At the qualifying affordable FAR of 5.01, the same lot reaches 50,100 sq ft. 50,100 / 680 = 73.68, so 73 units (ZR 23-22, 23-52).
• R4, 4,000 sq ft lot, not a qualifying residential site: 4,000 x 1.00 = 4,000 sq ft. 4,000 / 680 = 5.88, which rounds up to 6 units, because R4 without a suffix does not limit housing type (ZR 23-21, 22-122).

R1 to R5: the housing-type rule comes first

In low-density districts, the dwelling unit factor only matters where an apartment building is allowed at all. On zoning lots that are not qualifying residential sites, ZR 22-122 limits housing type: R1 and R2 allow only single-family detached residences; R3A, R3X, R4A and R5A allow only single- or two-family detached residences (R3A also zero lot line buildings); R3-1 and R4-1 allow only single- or two-family residences of certain types; and R4B allows only single- or two-family residences. In those cases the two-family limit, not the factor, decides the unit count. On qualifying residential sites in R1 to R5, any type of residence is permitted, and the factor then sets the cap (ZR 22-122). A qualifying residential site in R1 to R5 is defined in ZR 12-10; one path is a lot of at least 5,000 sq ft in the Greater Transit Zone with frontage on a wide street or the short end of a block, outside R1 and R2.

Common mistakes

• Using an old factor. Many older references and spreadsheets still carry pre-2024 factors that differed by district. The current text uses 680 throughout R1 to R12.
• Dividing built floor area instead of the maximum permitted residential floor area.
• Rounding every fraction up. Only fractions of three-quarters or more become a unit.
• Applying the factor in the Manhattan Core or Downtown Brooklyn, where it does not apply to residential developments or enlargements.

Dwelling unit factor FAQ

Related pages

• R6B zoning
• R7A zoning
• R5 zoning
• UAP explained
• What City of Yes changed
• ADU rules