Last edited 09 Oct 2020

Floor area ratio

The floor area ratio (FAR), also known as the plot ratio, is a measure of the total permitted floor area of a building, in relation to the total area of the lot (or plot) on which the building stands:

Gross floor area of all floors of the building / Area of the building lot = FAR

A higher ratio indicates a higher-density environment.

The concept emerged in Europe in the 19th century, and was then taken up in the USA in the 20th century as a form of zoning control for rapidly developing cities. FAR is now often used by urban planners, particularly in the USA, for assessing, or restricting, planning permissions, setting a limit on the 'load factor' generated by new developments, beyond which undue stress is placed on a city and its infrastructure.

A low permitted FAR may deter development, whilst a higher FAR allows more usable area, and hence higher potential sales.

The same FAR value can be achieved by buildings with varying numbers of storeys. For example:

1,000 sq. m building with one storey / 4,000 sq. m lot = 0.25

500 sq. m building with two storeys / 4,000 sq. m lot = 0.25

An FAR of 1.0 allows the developer to build a one-storey building over the lot, or a two-storey building over half the lot, or a three-storey building over one-third of the lot, and so on.

An FAR of 2.0 allows the developer to build a two-storey building over the lot, or a four-storey building over half, and so on.

Bradford City Centre Design Guide, Supplementary Planning Document, published in 2006, defines plot ratio as: ‘A measure of density for non-residential use. This is expressed as a ratio in which the first number relates to the floor area of the building and the second to the area of the site. A 2:1 ratio therefore denotes a building that has two times the floor area of the site. This could be a two storey building covering the entire site or a four storey building covering half of the site.’