Buildable Area Calculator

This calculator applies three independent zoning constraints and reports whichever one is most restrictive. Floor Area Ratio (FAR) caps total building square footage at Lot Area multiplied by the FAR value (Max GFA). Lot Coverage caps the building's footprint at a percentage of Lot Area (Max Footprint). Setbacks carve out a buildable rectangle from your lot's actual width and depth (Buildable Envelope), independent of the FAR and coverage percentages. Max Footprint is the smaller of Buildable Envelope and the lot-coverage limit, and Max Buildable Area is the smaller of Max GFA and that footprint multiplied by Max Stories -- so a generous FAR is worthless if setbacks leave too little footprint to build up from, and a wide-open lot is worthless if the FAR caps total floor area regardless of footprint.

Lot Area and Floor Area Ratio move Max Buildable Area by comparable proportions when FAR is the binding constraint, since Max GFA is their direct product. Side Setback moves the result in the opposite direction: every foot of required setback on each side removes it twice from the buildable width (once per side), which is why doubling side setbacks removes far more usable width than doubling front or rear setbacks alone. This tool applies a single flat FAR, coverage percentage, and setback distance uniformly -- real zoning codes often add bonus FAR for affordable housing, stepped setbacks that increase with building height, or separate rules for corner lots that this simplified model does not capture. Setback Area (Bounding Rectangle) is measured against Lot Width times Lot Depth, not against the separately-entered Lot Area -- a recorded lot's actual acreage frequently differs from a simple width-by-depth rectangle (irregular shape, easements, etc.), so this output tells you how much of the *rectangle implied by your width and depth entries* is consumed by setbacks, not how much of your recorded lot area that represents.