Buildable square footage is the maximum total floor area that zoning allows on a lot. It's calculated by multiplying the lot size by the FAR assigned to its zoning district.

In NYC, buildable SF is set by the Zoning Resolution and varies by district. A 5,000 SF lot in an R6A district (FAR 3.0) supports 15,000 buildable SF, while that same lot in an R8A district (FAR 6.02) supports 30,100 SF. The gap between what's allowed and what's already built is called unused FAR, or air rights. You can find any property's zoning district and FAR using the NYC Department of City Planning's ZoLa tool.

Developers price land based on what can be built on it, not by what is sitting on it. Buildable SF is the number that drives what a developer will pay. Many owners assume that number is locked in, but the City of Yes for Housing Opportunity (December 2024) increased allowable FAR in certain districts, meaning some properties carry more development potential today than they did a year ago.

If you don't know your buildable SF, you may not know what your property is actually worth.

Example: You own a 6,000 SF lot in an R8A district (FAR 6.02). Your lot supports 36,120 buildable SF. If your current building is only 9,000 SF, you're sitting on 27,120 SF of unused potential, which is what makes your property valuable to a developer.