By Zencalcy Editorial TeamLast reviewed About us
Floor area ratio is the zoning rule that ties building size to land size. A FAR of 0.5 on a 10,000 square foot lot allows 5,000 square feet of floor area spread across as many storeys as you like — one 5,000 square foot floor, or two of 2,500.
Allowed floor area from FAR, or FAR from a building.
floor area = lot area × FAR FAR = floor area ÷ lot area
FAR counts floor area across all storeys, while lot coverage counts the building footprint only. Garages, basements and some porches may be exempt from FAR under local codes — check the zoning ordinance before assuming.
| Symbol | Meaning |
|---|---|
| lot | Land area of the parcel. |
| FAR | Allowed floor area ratio. |
| A | Total floor area across storeys. |
10,000 × 0.5 = 5,000 square feet of floor area allowed — half an acre of building on the parcel.
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Suburban single-family zones run 0.2 to 0.5; urban rowhouse districts 1.0 to 2.5; dense downtown cores can allow 10 or more. The number, not the footprint limit, is what constrains most projects.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
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Content updated: September 2026