Planopedia

Floor area ratio (FAR) is a measurement that quantifies the intensity of development by calculating the ratio of a building's total floor area (or gross floor area) in proportion to the size of the piece of land upon which it is built. FAR is usually expressed as a decimal number.

Floor area ratio (FAR) is one of the most common regulatory metrics in city planning, and is thus critical to understanding how plans and zoning codes determine the future of the built environment. Zoning codes set the FAR at ratios commensurate with a desired outcome for future development—when FAR is larger, more, larger developments are desired. In the United States, however, FAR has most frequently been used to limit the intensity of land use or to control the mass and scale of development. 

In some cases a large FAR is considered a development incentive, and thus a tool of economic development. The allowable FAR set by zoning codes can vary greatly depending on the corresponding land use. So, for example, in many cities, the vast majority of residential zones are set for very low FARs, and the vast majority of the commercial and office uses allowed in the downtown area will have higher FARs. 

The first zoning codes were created to limit the bulk of buildings, but floor area ratio emerged later as an innovation in how zoning codes accomplished the goal of limiting development intensity. A Planning Advisory Services (PAS) report from the American Plan Association, published in 1958, explains more about the genesis of FAR as a common tool for plan implementation.   

Component Calculations

Because FAR is a ratio, understanding the term requires an understanding of the components of this ratio. 

To calculate FAR, the first component is a measurement of the buildable land area, measured by square feet, for the entire site, parcel, or lot. Buildable land area is the portion of a development site where construction can legally and reasonably occur. Many encroaching factors can limit the buildable land area, like public streets and other public rights-of-way, wetlands or streams, and regulatory limitations. Which regulatory implications and other encroachments determine the buildable land area is subject to some variety between specific, local zoning codes and land use regulations. 

The second calculation is determined by calculating the floor area, again in square feet, of each story of the building and then adding up the area of each floor to determine the gross, or total, floor area of the building.

Dividing the gross floor area by the buildable land area produces the Floor Area Ratio (FAR).

Without other development constraints, FAR would offer a great deal of flexibility in the final shape of a building. In many places in the United States and world, other regulations, such as height limits, will further limit how FAR can be apportioned in a development. 

Disclaimer

FAR is sometimes mistaken for density, but it's actually a measure of development intensity—the massing, volume, or bulk of buildings. 

Still, in limiting development intensity, FAR often has consequences for density. FAR often determines other considerations set in the zoning code, like parking requirements, residential units, and total load on municipal services, for example. Because FAR determines measurements of density, direct or indirect, sometimes FAR can be confused as synonymous with density. 

Some of the confusion might originate from the common practice in contemporary zoning codes to include programs that offer bonus FAR to developers that include or pay for some community resources, like public realm improvements, desirable uses (like healthcare or grocery stores), or affordable housing units. Most frequently, these programs are called density bonus programs, but the bonus delivered to participating developers is usually measured by FAR.

Controversies

Many industries and developers seek increased floor area ratios to enable more revenue generating space in a proposed development. Development opponents will seek to limit the floor area ratio, for fear of over-development, congestion, and scarce resources like police and fire services.

FAR has also faced more philosophical criticisms in planning history. The Congress for the New Urbanism, one of the leading reform movements in planning for the past several decades, rejects FAR as ineffective for planning and placemaking. The book Suburban Nation, by Andres Duany, Elizabeth Plater-Zyberk, and Jeff Speck, features some of these criticisms.