Residual FAR

Residual FAR is the difference between a lot's governing maximum FAR and its built FAR, floored at zero. Multiplied by lot area, it estimates the unused floor area the lot could add or transfer — the first approximation of development headroom, and the seed number of most air-rights and development-site conversations.

It is a paper ceiling, not a buildable figure: envelope rules and lot geometry decide how much of it can exist in three dimensions, prior recorded commitments may have spent it, and the governing maximum itself depends on use, street width, and overlays. Residual FAR is where the analysis starts, never where it ends.