Header image for Floor Area Ratio Calculator: FAR Formula & Example blog post

Floor Area Ratio Calculator, Formula and Example

Floor area ratio calculator

Divide the floor area counted under your local zoning rules by the lot area. Use the same area unit for both inputs. An optional permitted FAR shows the corresponding floor-area limit and the difference from your entered area.

Property area assumptions
Changing this label does not convert entered numbers.
Greater than zero; up to 1 trillion area units.
Zero or more; up to 1 trillion area units.
Enter a ratio, such as 2.5, rather than a percentage.

This is an arithmetic illustration, not confirmation of development rights. Local rules define counted floor area and lot area. Setbacks, height, lot coverage, parking and other controls may further restrict a project.

Last updated:

The FAR formula

FAR = counted floor area ÷ applicable lot area. Use the same area units for both inputs. The result is a ratio, not a percentage of ground covered and not a direct statement of permitted building height.

For example, New York City's Zoning Resolution defines FAR using total floor area on a zoning lot divided by that lot's area. Its separate definition of floor area determines what is counted. Other jurisdictions may use different terminology and inclusion rules. Check the relevant definitions and district provisions rather than assuming that an assessor's gross building area is the zoning numerator. See NYC Zoning Resolution definitions.

Worked example

Assume the applicable rules count a lot of 10,000 sq ft and allow a maximum FAR of 2.0. Assume there are no bonuses, transfers or other adjustments.

  • Maximum counted floor area under the FAR limit: 10,000 × 2.0 = 20,000 sq ft.
  • If an existing building has 15,000 sq ft of counted floor area, its FAR is 15,000 ÷ 10,000 = 1.5.
  • The arithmetic difference is 5,000 sq ft of counted floor area. That is not a promise that an addition is permitted or physically feasible.

Two counted floors of 10,000 sq ft and four counted floors of 5,000 sq ft both total 20,000 sq ft in this simplified example. Whether either arrangement is allowed depends on the other development rules and site conditions.

Lot area is not automatically the buildable footprint

A setback may restrict where a building can sit without necessarily reducing the lot area used in the FAR denominator. Rights-of-way, wetlands, zoning-lot arrangements and other conditions must be handled under the relevant rules. Do not automatically subtract every area where construction is constrained and call the remainder the FAR denominator.

Similarly, the treatment of parking, basements, mechanical space, balconies and other areas depends on local definitions. A measured gross or rentable figure used for leasing can differ from zoning floor area. Our floor-area guide explains why the purpose and definition of a measurement matter.

How to review a property's FAR

  1. Identify the parcel or zoning lot and the applicable zoning district.
  2. Confirm the lot-area definition and the floor-area inclusions and exclusions.
  3. Reconcile existing counted floor area with current plans and records.
  4. Identify the applicable FAR limit and any conditions on adjustments or bonuses.
  5. Review height, setbacks, lot coverage, use, access and other requirements with the appropriate planning or design professional.

FAR is one input to a development review. It does not by itself establish an entitlement, a unit count or a building envelope. Label marketing calculations with their sources and assumptions, and distinguish an illustrative capacity calculation from an approved development proposal.

Use CREOP's commercial real estate marketing software to organize verified site information, plans and supporting documents for a listing.