How to Calculate FAR (Floor Area Ratio)

Floor Area Ratio is the ratio between a building size and its lot size and can be used in zoning to control the bulk of buildings.


  • Step 1: Arrive at FAR, a decimal fraction, by dividing the gross floor area of the building by the total area of the lot. For example, if the gross floor area of the building is 10,000 feet and the total area of the lot is 15,000 feet, the FAR would be .66.
  • FACT: As of 2010, the building with the largest floor space in the world is Dubai International Airport's Terminal 3, with over 370 acres.
  • Step 2: Find the total area of the lot by multiplying the length of the site by the width.
  • TIP: Check with your district's planning department to find out specifics about what is included and excluded in their FAR calculations.
  • TIP: Only the portions of each story located above the ground surface are included.
  • Step 3: Include in the gross floor area any aboveground parking, either attached or detached, that is enclosed by two or more walls.
  • Step 4: Find the gross floor area of the building or buildings on a particular lot. Gross floor area includes all the covered space on the lot. Add together the plane surface of each story, measured between the exterior walls of the building.

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