Floor Area Ratio (FAR)

Floor Area Ratio (FAR) compares a building's counted floor area with the area of its lot. On a compact site, the ratio helps show whether allowed floor area is arranged as one broad level or stacked across stories. FAR measures floor area relative to land. It does not measure lot coverage, residential density, or livable square footage.

How FAR is calculated

The formula is:

FAR = total counted floor area ÷ lot area

A FAR of 1.0 means the counted floor area equals the lot area. A FAR of 0.5 means it equals half the lot area. A FAR of 2.0 means it equals twice the lot area. For example, a 10,000-square-foot lot with 20,000 square feet of counted floor area has a FAR of 2.0. A 5,000-square-foot lot with 10,000 square feet of counted floor area has the same ratio. FAR has no unit because both parts of the calculation measure area.

The applicable zoning code determines what counts as floor area, whether the measure is gross or net, which basements, parking areas, stairs, or attics are included or excluded, and what land area forms the lot basis. The American Planning Association describes FAR as floor area divided by lot area and notes that jurisdictions vary in what floor area includes. A local ordinance controls a real project's calculation, so do not apply a generic formula without checking its definitions.

What FAR changes on a small site

The same FAR can describe a broad one-story building or a narrower, taller building with several floors. The layouts produce different space constraints. Stacking floor area may preserve more ground-level open space, but it adds stairs, affects furniture movement, and changes daylight, privacy, and views. A wider building may reduce stairs while using more of the site.

Higher FAR may allow more homes or amenities where land is scarce. It can also increase perceived bulk, shadowing, infrastructure demand, and pressure on shared open space. FAR does not tell you how much of the counted area becomes storage, clear circulation, or comfortable living space. A building can meet a FAR limit while its internal layout still leaves too little storage or awkward circulation.

For a compact development or small home site, compare FAR with lot coverage, height, setbacks, open-space rules, parking requirements, residential density, and building-code requirements. These measures address different parts of the project.

FAR compared with density and livable area

Residential density counts homes or people per unit of land. FAR counts floor area per unit of land. A project can have a high FAR with a small number of large units, or a lower FAR with many small units. Treating FAR as a density measure can therefore misstate the number of homes.

Livable square footage answers another question. Depending on local rules and the building plan, FAR may include areas that are not living rooms, bedrooms, or usable storage. It may also exclude areas a resident experiences as part of the home. Check the counted-area definition, unit plans, circulation, storage, daylight, and amenity areas before estimating livable space.

A practical FAR check

For a property, identify the jurisdiction and the exact zoning provision. Record the lot area basis and the total counted floor area using the code's measurement method. List exclusions instead of assuming that a basement, parking area, stair, or attic is treated consistently everywhere. Then calculate the ratio and inspect each story. Note where stairs and circulation consume space, and whether the resulting units have adequate daylight, privacy, storage, and open space.

This avoids a common mistake: multiplying lot area by a published FAR number and treating the result as guaranteed livable space. The result is planning capacity under a particular definition, subject to other rules and the actual design. The APA's 1958 PAS Report 111 documents FAR's use in zoning and planning to regulate the relationship between building volume and land. That historical reference does not replace current local code review.