Floor Area Ratio

By Deane Barker • • tags: architecture, city-planning •

This is a zoning code formula that compares the total floor size of a building (all floors together) to the lot size it’s built on. There are rules around this number.

For example, if I want to build a 100-story building with each floor having 20,000 square feet of space, that’s a total of 2 million square feet of floor space. If the path of ground I want to build this on is 50,000 square feet, that’s a FAR of 40 (2 million / 50,000).

This is a basic measurement of density. The higher the FAR, the more activity the building will have in comparison to the land area it occupies.

Cities have rules around FAR. The allowable FAR depends on zoning district. For example, in New York City, R6 is residential. On narrow streets, the FAR is 2.00. Which means, if your lot size is 20 x 40, or 800 square feet, you can’t build anything with more than 1,600 square feet of total floor space. This prevents someone from building a skyscraper on residential land and claiming, “Hey, I stayed within my lot lines…”

The FAR can be increased if the developer adopts certain amenities. For example, if they have a greenspace or small park, they get a bonus to their FAR. Also, if they’re building lower-income housing, the FAR can be increased to keep those projects profitable.

Why I Looked It Up

It came up in The Heights: Anatomy of a Skyscraper.

Postscript

A video about why India has very few skyscrapers pointed to its very low FAR. Mumbai has historically had a FAR of only 1.3. The video compares this to other cities:

The video states that Mumbai’s low FAR was aimed at reducing congestion and limiting migrants. They’ve recently raised it to 2.5,

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