Floor Area Ratio (FAR) Calculator
Floor area ratio (FAR) is a building's total floor area divided by the area of its lot. Use the calculator below to find the FAR of an existing or planned building, or to find the maximum floor area your zoning allows on a lot.
FAR is also called floor space ratio (FSR) or plot ratio in some countries. The math is the same.
Calculate FAR
Calculate maximum buildable floor area
How to calculate FAR
Divide the total floor area of the building by the total area of the lot:
FAR = total building floor area / lot area
Add up the floor area of every story, not just the ground floor. A two-story building with 3,750 square feet on each floor has 7,500 square feet of floor area. On a 10,000 square foot lot, that is a FAR of 0.75.
How to calculate buildable area from FAR
Multiply the lot area by the maximum FAR in your zoning code. The result is the most floor area you can build in total, across all floors.
Maximum floor area = lot area x maximum FAR
| Lot area | Maximum FAR | Maximum floor area | One story | Two stories |
|---|---|---|---|---|
| 6,000 sq ft | 0.5 | 3,000 sq ft | 3,000 sq ft footprint | 1,500 sq ft per floor |
| 10,000 sq ft | 1.0 | 10,000 sq ft | 10,000 sq ft footprint | 5,000 sq ft per floor |
| 20,000 sq ft | 2.0 | 40,000 sq ft | Not possible on one floor | 20,000 sq ft per floor |
FAR is only one limit. Your building also has to fit within the setbacks, the height limit and the maximum lot coverage, so the real buildable area can be smaller than the FAR number.
What counts as floor area?
Each zoning code defines floor area in its own way. Most count all enclosed, finished space on every story. Many leave out basements that are mostly below ground, parking garages, stairwells and mechanical rooms. Read the definition of "floor area" or "gross floor area" in your local ordinance before you rely on a number.
What is a good FAR?
There is no single good FAR. It depends on what the zone allows. Low-density residential zones often cap FAR well below 1.0, which keeps houses small relative to their lots. Dense downtown districts can allow a FAR of 10 or more, which is how tall towers fit on small lots.
For a buyer or developer, the useful comparison is the FAR a building has now against the maximum the zone allows. If a lot is built well below its maximum FAR, there may be room to add floor area.
FAR vs lot coverage
FAR limits the total floor area on every story combined. Lot coverage limits only the building footprint, the share of the lot covered by structures. A two-story house can meet a 40% lot coverage limit and still break a 0.5 FAR limit, so check both.
You can read more about how planners use the ratio in the Wikipedia article on floor area ratio. To find the maximum FAR for your property, look up your city's zoning map and code on ZoningPoint.
Frequently asked questions
What is floor area ratio?
Floor area ratio (FAR) is the total floor area of a building divided by the area of the lot it sits on. A 10,000 square foot building on a 5,000 square foot lot has a FAR of 2.0. Zoning codes use a maximum FAR to cap how much building a lot can hold.
How do I calculate buildable area from FAR?
Multiply the lot area by the maximum FAR in your zoning code. A 6,000 square foot lot with a maximum FAR of 0.5 can have up to 3,000 square feet of floor area, spread across as many floors as the height limit allows.
Is floor space ratio (FSR) the same as FAR?
Yes. Floor space ratio (FSR), plot ratio and floor area ratio all describe the same thing: building floor area divided by lot area. Australia commonly says FSR, the UK and Singapore often say plot ratio, and U.S. zoning codes say FAR.
Does a basement or garage count toward FAR?
It depends on the local code. Many codes exclude basements that are mostly below grade, parking garages and mechanical rooms from floor area, while others count them. Check the definition of floor area in your zoning ordinance before you run the numbers.
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