How often the formula is wrong
We compared PLUTO's lot area × residential FAR with the largest zoning floor area RunEnvelope's engine could place in a market-rate residential scheme on the same lot, after yards, height and setback, lot coverage and every other bulk rule.
| Manhattan lots | By more than 10% | By more than 25% |
|---|---|---|
| All lots measured | 5.0% | 2.2% |
| Inside special districts | 12.1% | not measured |
Method: RunEnvelope has run its current engine on 96% of Manhattan lots; the figures cover the 38,530 of them with a residential FAR and at least 1,000 sf of lot area. PLUTO 26v2, measured 2026-10-26. Engine figure is the maximum zoning floor area across market-rate residential schemes, excluding bonus, UAP, AIRS, shared housing (SRO) and plaza schemes, compared with PLUTO lot area × residential FAR. The other boroughs are not yet covered densely enough by the current engine to report.
Read the other way, for about 19 in 20 Manhattan lots the formula lands within 10 percent of what a market-rate residential building can hold. Special districts are where it most often misleads: they layer their own height, setback, street wall and floor area rules on the underlying district, and a single FAR figure cannot capture all of that.
The honest reading
Three published lots where it falls short
Every RunEnvelope lot page prints both numbers. These three are among the lots where the engine's largest residential-only scheme without an affordability obligation comes in well under PLUTO's FAR times the lot area.
| Lot | Zoning | Frontage × depth | Lot area × PLUTO FAR | Engine, residential (no affordability) | Share |
|---|---|---|---|---|---|
| 3410 Broadway, Manhattan | R8 | 199.83 × 34 ft | 6,797 sf × 6.02 = 40,918 sf | 29,254 sf | 71% |
| 611 8 Avenue, Manhattan | C6-4 | 39.5 × 100 ft | 3,950 sf × 10.00 = 39,500 sf | 26,160 sf | 66% |
| 59-01 Main Street, Queens | R5B | 196 × 91.5 ft | 27,260 sf × 1.50 = 40,890 sf | 37,437 sf | 92% |
Figures as printed on each lot page. The full study names which rule binds on each lot.
The shapes tell the story. One is a corner lot only 34 feet deep; one is a 39.5-foot-wide interior lot where the residential scheme follows a sky exposure plane; one is a large irregular corner lot with nearly 200 feet of frontage in a low-density district. None of that is visible in a lot area and an FAR.
Worked example: buying air rights you cannot use
Return to the two R7A lots from Part 2: lot A, 50 × 100 ft, vacant, on a narrow street; lot B next door keeps a 4,000 sf building. After the merger lot A may hold 36,000 sf on paper. Here is what the R7A envelope allows on lot A, floor by floor:
- ■Rear yard: lot width 40 feet or more, so 20 feet at or below 75 feet and 30 feet above (ZR 23-342).
- ■Lot coverage: 80 percent on an interior lot (ZR 23-362), so 4,000 sf on lot A.
- ■Height: base height 40 to 75 feet, maximum 85 feet for standard residences (ZR 23-432).
- ■Setback: 15 feet from a narrow-street wall above the base (ZR 23-433).
| Floor | Height | Plate depth | Floor area |
|---|---|---|---|
| 1 | 0 to 10 ft | 80 ft | 4,000 sf |
| 2 | 10 to 20 ft | 80 ft | 4,000 sf |
| 3 | 20 to 30 ft | 80 ft | 4,000 sf |
| 4 | 30 to 40 ft | 80 ft | 4,000 sf |
| 5 | 40 to 50 ft | 80 ft | 4,000 sf |
| 6 | 50 to 60 ft | 80 ft | 4,000 sf |
| 7 | 60 to 70 ft | 80 ft | 4,000 sf |
| 8 | 70 to 80 ft | 55 ft | 2,750 sf |
| Total | 30,750 sf |
An upper bound: street wall on the street line, no courts, no articulation, and any floor reaching above a threshold takes that threshold's rule. A real design holds less.
- Lot A alone, lot area × FAR
- 20,000 sf
- Floor area bought through the merger
- 16,000 sf
- Lot A after the merger, on paper
- 36,000 sf
- What lot A's envelope can hold
- 30,750 sf
- Purchased floor area that fits
- 10,750 sf (67%)
- Purchased floor area that does not
- 5,250 sf
Lot A on its own is fine: its 20,000 sf fits with room to spare, the common case in the table above. The trouble starts when floor area is added. A buyer who prices all 16,000 sf pays for 5,250 sf it cannot build, and Part 3 shows what that does to the price per usable foot.
There are ways to recover some of it: the qualifying affordable heights in Part 6, or bulk relief where a special permit or authorization is available. Each one has to be modeled, not assumed.
Three more gaps the formula ignores
- ■Zoning floor area is not sellable area. Floor area is measured from the exterior faces of exterior walls and excludes items such as cellar space (ZR 12-10), while City of Yes lets some amenity and corridor space be exempted (ZR 23-23). Gross building area, rentable area and sellable area are each a different number from zoning floor area.
- ■Units are capped separately. The maximum number of dwelling units is residential floor area divided by 680 (ZR 23-52). Extra floor area may add larger apartments rather than more of them.
- ■Floor plates that fit but do not work. On a narrow lot, stairs, an elevator and a corridor take a large share of each floor, and windows need distance from lot lines (ZR 23-372). On RunEnvelope's 159 Ludlow Street sample, a 1,063 sf lot, several scenarios name floor-plate efficiency, not FAR, as the binding constraint.
Before you buy land or air rights
- 01
Model the envelope with the floor area you are buying
Not the receiving lot as it is today: the lot with the transfer, the merged zoning lot's coverage and the yards that apply to it. - 02
Price only the floor area that fits
Agree the price on usable floor area, or make the deal conditional on the zoning calculations. - 03
Check the lot's special rules
Special district, split district (ZR 77-22), historic district and landmark status each move the answer. In Manhattan, lots inside special districts are overstated by more than 10 percent more than twice as often as lots overall.
Check it free
Sources, checked 2026-10-26
- ZR 23-22, Floor area regulations for R6 through R12 districts
- ZR 23-342, Rear yard requirements
- ZR 23-362, Maximum lot coverage in R6 through R12 districts
- ZR 23-432, Height and setback requirements (R6 through R12)
- ZR 23-433, Standard setback regulations
- ZR 12-10, Definitions: zoning lot, floor area, floor area ratio, party in interest
- ZR 23-23, Special floor area provisions for multiple dwelling residences
- ZR 23-52, Maximum number of dwelling units
- ZR 23-372, Distance between legally required windows and lot lines
- ZR 77-22, Floor area ratio on split zoning lots
- NYC Department of City Planning, PLUTO and MapPLUTO
Not legal advice. This guide explains the Zoning Resolution in plain English and can be out of date the day the text is amended. Before you price, buy or sell development rights, have a land use attorney and the filing architect confirm the zoning lot, the documents and the numbers.